mxml/doc/body.md

---
title: Mini-XML 4.0 Programming Manual
author: Michael R Sweet
copyright: Copyright © 2003-2024, All Rights Reserved.
version: 4.0
...

Introduction
============

Mini-XML is a small XML parsing library that you can use to read XML data files
or strings in your application without requiring large non-standard libraries.
Mini-XML provides the following functionality:

- Reading of UTF-8 and UTF-16 and writing of UTF-8 encoded XML files and
  strings.
- Data is stored in a linked-list tree structure, preserving the XML data
  hierarchy.
- SAX (streamed) reading of XML files and strings to minimize memory usage.
- Supports arbitrary element names, attributes, and attribute values with no
  preset limits, just available memory.
- Supports integer, real, opaque ("CDATA"), text, and custom data types in
  "leaf" nodes.
- Functions for creating and managing trees of data.
- "Find" and "walk" functions for easily locating and navigating trees of
  data.

Mini-XML doesn't do validation or other types of processing on the data based
upon schema files or other sources of definition information.


History
-------

Mini-XML was initially developed for the [Gutenprint](http://gutenprint.sf.net/)
project to replace the rather large and unwieldy `libxml2` library with
something substantially smaller and easier-to-use.  It all began one morning in
June of 2003 when Robert posted the following sentence to the developer's list:

> It's bad enough that we require libxml2, but rolling our own XML parser is a
> bit more than we can handle.

I then replied with:

> Given the limited scope of what you use in XML, it should be trivial to code a
> mini-XML API in a few hundred lines of code.

I took my own challenge and coded furiously for two days to produce the initial
public release of Mini-XML, total lines of code: 696.  Robert promptly
integrated Mini-XML into Gutenprint and removed libxml2.

Thanks to lots of feedback and support from various developers, Mini-XML has
evolved since then to provide a more complete XML implementation and now stands
at a whopping 3,875 lines of code, compared to 175,808 lines of code for libxml2
version 2.11.7.


Resources
---------

The Mini-XML home page can be found at <https://www.msweet.org/mxml>.  From
there you can download the current version of Mini-XML, access the issue
tracker, and find other resources.

Mini-XML v4 has a slightly different API than prior releases. See the
[Migrating from Mini-XML v3.x](@) chapter for details.


Legal Stuff
-----------

The Mini-XML library is copyright © 2003-2024 by Michael R Sweet and is provided
under the Apache License Version 2.0 with an (optional) exception to allow
linking against GPL2/LGPL2-only software.  See the files "LICENSE" and "NOTICE"
for more information.


Using Mini-XML
==============

Mini-XML provides a single header file which you include:

```c
#include <mxml.h>
```

The Mini-XML library is included with your program using the `-lmxml4` option:

    gcc -o myprogram myprogram.c -lmxml4

If you have the `pkg-config` software installed, you can use it to determine the
proper compiler and linker options for your installation:

    gcc `pkg-config --cflags mxml4` -o myprogram myprogram.c `pkg-config --libs mxml4`

> Note: The library name "mxml4" is a configure-time option. If you use the
> `--disable-libmxml4-prefix` configure option the library is named "mxml".


Loading an XML File
-------------------

You load an XML file using the [mxmlLoadFile](@@) function:

```c
mxml_node_t *
mxmlLoadFilename(mxml_node_t *top, const char *filename,
                 mxml_load_cb_t load_cb, void *load_cbdata,
                 mxml_sax_cb_t sax_cb, void *sax_cbdata);
```

The `load_cb` argument specifies a function that assigns child (value) node
types for each element in the document.  The default callback (`NULL`) supports
passing a pointer to an `mxml_type_t` variable containing the type of value
nodes.  For example, to load the XML file "filename.xml" containing literal
strings you can use:

```c
mxml_node_t *tree;
mxml_type_t type = MXML_TYPE_OPAQUE;

tree = mxmlLoadFilename(/*top*/NULL, "filename.xml",
                        /*load_cb*/NULL, /*load_cbdata*/&type,
                        /*sax_cb*/NULL, /*sax_cbdata*/NULL);
```

Mini-XML also provides functions to load from a `FILE` pointer, a file
descriptor, or string:

```c
mxml_node_t *
mxmlLoadFd(mxml_node_t *top, int fd,
           mxml_load_cb_t load_cb, void *load_cbdata,
           mxml_sax_cb_t sax_cb, void *sax_cbdata);

mxml_node_t *
mxmlLoadFile(mxml_node_t *top, FILE *fp,
             mxml_load_cb_t load_cb, void *load_cbdata,
             mxml_sax_cb_t sax_cb, void *sax_cbdata);

mxml_node_t *
mxmlLoadString(mxml_node_t *top, const char *s,
           mxml_load_cb_t load_cb, void *load_cbdata,
           mxml_sax_cb_t sax_cb, void *sax_cbdata);
```


### Load Callbacks

The `load_xxx` arguments to the mxmlLoadXxx functions are a callback function
and a data pointer which are used to determine the value type of each data node
in an XML document.  The default (`NULL`) callback expects the `load_cbdata`
argument to be a pointer to a `mxml_type_t` variable that contains the desired
value node type - if `NULL`, it uses the `MXML_TYPE_TEXT` (whitespace-separated
text) type.

You can provide your own callback function for more complex XML documents. Your
callback function will receive a pointer to the current element node and must
return the value type of the immediate children for that element node:
`MXML_TYPE_CUSTOM`, `MXML_TYPE_INTEGER`, `MXML_TYPE_OPAQUE`, `MXML_TYPE_REAL`,
or `MXML_TYPE_TEXT`.  The function is called *after* the element and its
attributes have been read so you can look at the element name, attributes, and
attribute values to determine the proper value type to return.

The following callback function looks for an attribute named "type" or the
element name to determine the value type for its child nodes:

```c
mxml_type_t
my_load_cb(void *cbdata, mxml_node_t *node)
{
  const char *type;

 /*
  * You can lookup attributes and/or use the element name,
  * hierarchy, etc...
  */

  type = mxmlElementGetAttr(node, "type");
  if (type == NULL)
    type = mxmlGetElement(node);
  if (type == NULL)
    type = "text";

  if (!strcmp(type, "integer"))
    return (MXML_TYPE_INTEGER);
  else if (!strcmp(type, "opaque"))
    return (MXML_TYPE_OPAQUE);
  else if (!strcmp(type, "real"))
    return (MXML_TYPE_REAL);
  else
    return (MXML_TYPE_TEXT);
}
```

To use this callback function, simply specify it when you call any of the load
functions:

```c
mxml_node_t *tree;

tree = mxmlLoadFilename(/*top*/NULL, "filename.xml",
                        my_load_cb, /*load_cbdata*/NULL,
                        /*sax_cb*/NULL, /*sax_cbdata*/NULL);
```


Nodes
-----

Every piece of information in an XML file is stored in memory in "nodes".  Nodes
are defined by the `mxml_node_t` structure.  Each node has a typed value,
optional user data, a parent node, sibling nodes (previous and next), and
potentially child nodes.

For example, if you have an XML file like the following:

    <?xml version="1.0" encoding="utf-8"?>
    <data>
        <node>val1</node>
        <node>val2</node>
        <node>val3</node>
        <group>
            <node>val4</node>
            <node>val5</node>
            <node>val6</node>
        </group>
        <node>val7</node>
        <node>val8</node>
    </data>

the node tree for the file would look like the following in memory:

    ?xml version="1.0" encoding="utf-8"?
      |
    data
      |
    node - node - node - group - node - node
      |      |      |      |       |      |
    val1   val2   val3     |     val7   val8
                           |
                         node - node - node
                           |      |      |
                         val4   val5   val6

where "-" is a pointer to the sibling node and "|" is a pointer to the first
child or parent node.

The [mxmlGetType](@@) function gets the type of a node:

```c
mxml_type_t
mxmlGetType(mxml_node_t *node);
```

- `MXML_TYPE_CDATA` : CDATA,
- `MXML_TYPE_COMMENT` : A comment,
- `MXML_TYPE_CUSTOM` : A custom value defined by your application,
- `MXML_TYPE_DECLARATION` : A declaration such as `<!DOCTYPE html>`,
- `MXML_TYPE_DIRECTIVE` : A processing instruction such as
  `<?xml version="1.0"?>`,
- `MXML_TYPE_ELEMENT` : An XML element,
- `MXML_TYPE_INTEGER` : A whitespace-delimited integer value,
- `MXML_TYPE_OPAQUE` : An opaque string value that preserves all whitespace,
- `MXML_TYPE_REAL` : A whitespace-delimited floating point value, or
- `MXML_TYPE_TEXT` : A whitespace-delimited text (fragment) value.

The parent and sibling nodes are accessed using the [mxmlGetParent](@@),
[mxmlGetNextSibling](@@), and [mxmlGetPreviousSibling](@@) functions, while the
children of an element node are accessed using the [mxmlGetFirstChild](@@) or
[mxmlGetLastChild](@@) functions:

```c
mxml_node_t *
mxmlGetFirstChild(mxml_node_t *node);

mxml_node_t *
mxmlGetLastChild(mxml_node_t *node);

mxml_node_t *
mxmlGetNextSibling(mxml_node_t *node);

mxml_node_t *
mxmlGetParent(mxml_node_t *node);

mxml_node_t *
mxmlGetPrevSibling(mxml_node_t *node);
```

The [mxmlGetUserData](@@) function gets any user (application) data associated
with the node:

```c
void *
mxmlGetUserData(mxml_node_t *node);
```


Creating XML Documents
----------------------

You can create and update XML documents in memory using the various mxmlNewXxx
functions. The following code will create the XML document described in the
previous section:

```c
mxml_node_t *xml;    /* <?xml version="1.0"?> */
mxml_node_t *data;   /* <data> */
mxml_node_t *node;   /* <node> */
mxml_node_t *group;  /* <group> */

xml = mxmlNewXML("1.0");

data = mxmlNewElement(xml, "data");

    node = mxmlNewElement(data, "node");
    mxmlNewText(node, false, "val1");
    node = mxmlNewElement(data, "node");
    mxmlNewText(node, false, "val2");
    node = mxmlNewElement(data, "node");
    mxmlNewText(node, false, "val3");

    group = mxmlNewElement(data, "group");

        node = mxmlNewElement(group, "node");
        mxmlNewText(node, false, "val4");
        node = mxmlNewElement(group, "node");
        mxmlNewText(node, false, "val5");
        node = mxmlNewElement(group, "node");
        mxmlNewText(node, false, "val6");

    node = mxmlNewElement(data, "node");
    mxmlNewText(node, false, "val7");
    node = mxmlNewElement(data, "node");
    mxmlNewText(node, false, "val8");
```

We start by creating the declaration node common to all XML files using the
[mxmlNewXML](@@) function:

```c
xml = mxmlNewXML("1.0");
```

We then create the `<data>` node used for this document using the
[mxmlNewElement](@@) function.  The first argument specifies the parent node
\(`xml`) while the second specifies the element name \(`data`):

```c
data = mxmlNewElement(xml, "data");
```

Each `<node>...</node>` in the file is created using the [mxmlNewElement](@@)
and [mxmlNewText](@@) functions.  The first argument of [mxmlNewText](@@)
specifies the parent node \(`node`).  The second argument specifies whether
whitespace appears before the text - `false` in this case.  The last argument
specifies the actual text to add:

```c
node = mxmlNewElement(data, "node");
mxmlNewText(node, false, "val1");
```

The resulting in-memory XML document can then be saved or processed just like
one loaded from disk or a string.


Saving an XML File
------------------

You save an XML file using the [mxmlSaveFilename](@@) function:

```c
bool
mxmlSaveFilename(mxml_node_t *node, const char *filename,
                 mxml_save_cb_t cb, void *cbdata);
```

The `cb` and `cbdata` arguments specify a function and data pointer that is
called to determine what whitespace (if any) is inserted before and after each
element node.  A `NULL` value tells Mini-XML to not include any extra
whitespace.  For example, so save an XML file to the file "filename.xml" with
no extra whitespace:

```c
mxmlSaveFile(xml, "filename.xml", /*cb*/NULL, /*cbdata*/NULL);
```

Mini-XML also provides functions to save to a file descriptor, `FILE` pointer,
or strings:

```c
char *
mxmlSaveAllocString(mxml_node_t *node, mxml_save_cb_t cb,
                    void *cbdata);

bool
mxmlSaveFd(mxml_node_t *node, int fd, mxml_save_cb_t cb,
           void *cbdata);

bool
mxmlSaveFile(mxml_node_t *node, FILE *fp, mxml_save_cb_t cb,
             void *cbdata);

size_t
mxmlSaveString(mxml_node_t *node, char *buffer, size_t bufsize,
               mxml_save_cb_t cb, void *cbdata);
```


### Controlling Line Wrapping

When saving XML documents, Mini-XML normally wraps output lines at column 75 so
that the text is readable in terminal windows.  The [mxmlSetWrapMargin](@@)
function overrides the default wrap margin for the current thread:

```c
void mxmlSetWrapMargin(int column);
```

For example, the following code sets the margin to 132 columns:

```c
mxmlSetWrapMargin(132);
```

while the following code disables wrapping by setting the margin to 0:

```c
mxmlSetWrapMargin(0);
```


### Save Callbacks

The last arguments to the mxmlSaveXxx functions are a callback function and data
pointer which is used to automatically insert whitespace in an XML document.
Your callback function will be called up to four times for each element node
with a pointer to the node and a `where` value of `MXML_WS_BEFORE_OPEN`, `MXML_WS_AFTER_OPEN`, `MXML_WS_BEFORE_CLOSE`, or `MXML_WS_AFTER_CLOSE`.  The
callback function should return `NULL` if no whitespace should be added or the
string to insert (spaces, tabs, carriage returns, and newlines) otherwise.

The following whitespace callback can be used to add whitespace to XHTML output
to make it more readable in a standard text editor:

```c
const char *
whitespace_cb(void *cbdata, mxml_node_t *node, mxml_ws_t where)
{
  const char *element;

 /*
  * We can conditionally break to a new line before or after
  * any element.  These are just common HTML elements...
  */

  element = mxmlGetElement(node);

  if (!strcmp(element, "html") ||
      !strcmp(element, "head") ||
      !strcmp(element, "body") ||
      !strcmp(element, "pre") ||
      !strcmp(element, "p") ||
      !strcmp(element, "h1") ||
      !strcmp(element, "h2") ||
      !strcmp(element, "h3") ||
      !strcmp(element, "h4") ||
      !strcmp(element, "h5") ||
      !strcmp(element, "h6"))
  {
   /*
    * Newlines before open and after close...
    */

    if (where == MXML_WS_BEFORE_OPEN ||
        where == MXML_WS_AFTER_CLOSE)
      return ("\n");
  }
  else if (!strcmp(element, "dl") ||
           !strcmp(element, "ol") ||
           !strcmp(element, "ul"))
  {
   /*
    * Put a newline before and after list elements...
    */

    return ("\n");
  }
  else if (!strcmp(element, "dd") ||
           !strcmp(element, "dt") ||
           !strcmp(element, "li"))
  {
   /*
    * Put a tab before <li>'s, <dd>'s, and <dt>'s, and a
    * newline after them...
    */

    if (where == MXML_WS_BEFORE_OPEN)
      return ("\t");
    else if (where == MXML_WS_AFTER_CLOSE)
      return ("\n");
  }

 /*
  * Otherwise return NULL for no added whitespace...
  */

  return (NULL);
}
```

To use this callback function, simply use the name when you call any of the save
functions:

```c
FILE *fp;
mxml_node_t *tree;

fp = fopen("filename.xml", "w");
mxmlSaveFile(tree, fp, whitespace_cb, /*cbdata*/NULL);
fclose(fp);
```


Memory Management
-----------------

Once you are done with the XML data, use the [mxmlDelete](@@) function to
free the memory that is used for a particular node and its children:

```c
void
mxmlDelete(mxml_node_t *tree);
```

You can also use reference counting to manage memory usage.  The
[mxmlRetain](@@) and [mxmlRelease](@@) functions increment and decrement a
node's use count, respectively.  When the use count goes to zero,
[mxmlRelease](@@) calls [mxmlDelete](@@) to actually free the memory used by the
node tree.  New nodes start with a use count of `1`.


More About Nodes
================

Element Nodes
-------------

Element \(`MXML_TYPE_ELEMENT`) nodes are created using the [mxmlNewElement](@@)
function.  Element attributes are set using the [mxmlElementSetAttr](@@) and
[mxmlElementSetAttrf](@@) functions and cleared using the
[mxmlElementClearAttr](@@) function:

```c
mxml_node_t *
mxmlNewElement(mxml_node_t *parent, const char *name);

void
mxmlElementClearAttr(mxml_node_t *node, const char *name);

void
mxmlElementSetAttr(mxml_node_t *node, const char *name,
                   const char *value);

void
mxmlElementSetAttrf(mxml_node_t *node, const char *name,
                    const char *format, ...);
```

The [mxmlGetElement](@@) function retrieves the element name while the
[mxmlElementGetAttr](@@) function retrieves the value string for a named
attribute associated with the element.  The [mxmlElementGetAttrByIndex](@@) and
[mxmlElementGetAttrCount](@@) functions retrieve attributes by index:

```c
const char *
mxmlGetElement(mxml_node_t *node);

const char *
mxmlElementGetAttr(mxml_node_t *node, const char *name);

const char *
mxmlElementGetAttrByIndex(mxml_node_t *node, size_t idx,
                          const char **name);

size_t
mxmlElementGetAttrCount(mxml_node_t *node);
```


CDATA Nodes
-----------

CDATA \(`MXML_TYPE_CDATA`) nodes are created using the [mxmlNewCDATA](@@)
and [mxmlNewCDATAf](@@) functions:

```c
mxml_node_t *
mxmlNewCDATA(mxml_node_t *parent, const char *string);

mxml_node_t *
mxmlNewCDATAf(mxml_node_t *parent, const char *format, ...);
```

The [mxmlGetCDATA](@@) function retrieves the CDATA string pointer for a node:

```c
const char *
mxmlGetCDATA(mxml_node_t *node);
```


Comment Nodes
-------------

Comment \(`MXML_TYPE_COMMENT`) nodes are created using the [mxmlNewComment](@@)
and [mxmlNewCommentf](@@) functions, for example:

```c
mxml_node_t *node = mxmlNewComment(" This is a comment ");

mxml_node_t *node = mxmlNewCommentf(" This is comment %d ", 42);
```

Similarly, the [mxmlGetComment](@@) function retrieves the comment string
pointer for a node:

```c
const char *comment = mxmlGetComment(node);
/* returns " This is a comment " */
```


Processing Instruction Nodes
----------------------------

Processing instruction \(`MXML_TYPE_DIRECTIVE`) nodes are created using the
[mxmlNewDirective](@@) and [mxmlNewDirectivef](@@) functions:

```c
mxml_node_t *node = mxmlNewDirective("xml-stylesheet type=\"text/css\" href=\"style.css\"");

mxml_node_t *node = mxmlNewDirectivef("xml version=\"%s\"", version);
```

The [mxmlGetDirective](@@) function retrieves the processing instruction string
for a node:

```c
const char *instr = mxmlGetElement(node);
/* returns "xml-stylesheet type=\"text/css\" href=\"style.css\"" */
```

The [mxmlNewXML](@@) function can be used to create the top-level "xml"
processing instruction with an associated version number:

```c
mxml_node_t *
mxmlNewXML(const char *version);
```


Integer Nodes
-------------

Integer \(`MXML_TYPE_INTEGER`) nodes are created using the [mxmlNewInteger](@@)
function:

```c
mxml_node_t *
mxmlNewInteger(mxml_node_t *parent, long integer);
```

The [mxmlGetInteger](@@) function retrieves the integer value for a node:


```c
long
mxmlGetInteger(mxml_node_t *node);
```


Opaque String Nodes
-------------------

Opaque string \(`MXML_TYPE_OPAQUE`) nodes are created using the
[mxmlNewOpaque](@@) and [mxmlNewOpaquef](@@) functions:

```c
mxml_node_t *
mxmlNewOpaque(mxml_node_t *parent, const char *opaque);

mxml_node_t *
mxmlNewOpaquef(mxml_node_t *parent, const char *format, ...);
```

The [mxmlGetOpaque](@@) function retrieves the opaque string pointer for a node:

```c
const char *
mxmlGetOpaque(mxml_node_t *node);
```


Text Nodes
----------

Whitespace-delimited text string \(`MXML_TYPE_TEXT`) nodes are created using the
[mxmlNewText](@@) and [mxmlNewTextf](@@) functions.  Each text node consists of
a text string and (leading) whitespace boolean value.

```c
mxml_node_t *
mxmlNewText(mxml_node_t *parent, bool whitespace,
            const char *string);

mxml_node_t *
mxmlNewTextf(mxml_node_t *parent, bool whitespace,
             const char *format, ...);
```

The [mxmlGetText](@@) function retrieves the text string pointer and whitespace
boolean value for a node:

```c
const char *
mxmlGetText(mxml_node_t *node, bool *whitespace);
```


Real Number Nodes
--------------------

Real number \(`MXML_TYPE_REAL`) nodes are created using the [mxmlNewReal](@@)
function:

```c
mxml_node_t *
mxmlNewReal(mxml_node_t *parent, double real);
```

The [mxmlGetReal](@@) function retrieves the real number for a node:

```c
double
mxmlGetReal(mxml_node_t *node);
```


Locating Data in an XML Document
================================

Mini-XML provides many functions for enumerating, searching, and indexing XML
documents.


Finding Nodes
-------------

The [mxmlFindPath](@@) function finds the (first) value node under a specific
element using a "path":

```c
mxml_node_t *
mxmlFindPath(mxml_node_t *node, const char *path);
```

The `path` string can contain the "*" wildcard to match a single element node in
the hierarchy.  For example, the following code will find the first "node"
element under the "group" element, first using an explicit path and then using a
wildcard:

```c
mxml_node_t *value = mxmlFindPath(xml, "data/group/node");

mxml_node_t *value = mxmlFindPath(xml, "data/*/node");
```

The [mxmlFindElement](@@) function can be used to find a named element,
optionally matching an attribute and value:

```c
mxml_node_t *
mxmlFindElement(mxml_node_t *node, mxml_node_t *top,
                const char *element, const char *attr,
                const char *value, int descend);
```

The "element", "attr", and "value" arguments can be passed as `NULL` to act as
wildcards, e.g.:

```c
/* Find the first "a" element */
node = mxmlFindElement(tree, tree, "a", NULL, NULL,
                       MXML_DESCEND_ALL);

/* Find the first "a" element with "href" attribute */
node = mxmlFindElement(tree, tree, "a", "href", NULL,
                       MXML_DESCEND_ALL);

/* Find the first "a" element with "href" to a URL */
node = mxmlFindElement(tree, tree, "a", "href",
                       "http://msweet.org/",
                       MXML_DESCEND_ALL);

/* Find the first element with a "src" attribute*/
node = mxmlFindElement(tree, tree, NULL, "src", NULL,
                       MXML_DESCEND_ALL);

/* Find the first element with a "src" = "foo.jpg" */
node = mxmlFindElement(tree, tree, NULL, "src", "foo.jpg",
                       MXML_DESCEND_ALL);
```

You can also iterate with the same function:

```c
mxml_node_t *node;

for (node = mxmlFindElement(tree, tree, "element", NULL,
                            NULL, MXML_DESCEND_ALL);
     node != NULL;
     node = mxmlFindElement(node, tree, "element", NULL,
                            NULL, MXML_DESCEND_ALL))
{
  ... do something ...
}
```

The `descend` argument \(`MXML_DESCEND_ALL` in the examples above) can be one of
three constants:

- `MXML_DESCEND_NONE`: ignore child nodes in the element hierarchy, instead
  using siblings (same level) or parent nodes (above) until the top (root) node
  is reached.

- `MXML_DESCEND_FIRST`: start the search with the first child of the node, and
  then search siblings.  You'll normally use this when iterating through direct
  children of a parent node, e.g. all of the "node" and "group" elements under
  the "?xml" parent node in the previous example.

- `MXML_DESCEND_ALL`: search child nodes first, then sibling nodes, and then
  parent nodes.


Iterating Nodes
---------------

While the [mxmlFindNode](@@) and [mxmlFindPath](@@) functions will find a
particular element node, sometimes you need to iterate over all nodes.  The
[mxmlWalkNext](@@) and [mxmlWalkPrev](@@) functions can be used to iterate
through the XML node tree:

```c
mxml_node_t *
mxmlWalkNext(mxml_node_t *node, mxml_node_t *top,
             int descend);

mxml_node_t *
mxmlWalkPrev(mxml_node_t *node, mxml_node_t *top,
             int descend);
```

Depending on the value of the `descend` argument, these functions will
automatically traverse child, sibling, and parent nodes until the `top` node is
reached.  For example, the following code will iterate over all of the nodes in
the sample XML document in the previous section:

```c
mxml_node_t *node;

for (node = xml;
     node != NULL;
     node = mxmlWalkNext(node, xml, MXML_DESCEND_ALL))
{
  ... do something ...
}
```

The nodes will be returned in the following order:

```
<?xml version="1.0" encoding="utf-8"?>
<data>
<node>
val1
<node>
val2
<node>
val3
<group>
<node>
val4
<node>
val5
<node>
val6
<node>
val7
<node>
val8
```


Indexing
--------

The [mxmlIndexNew](@@) function allows you to create an index of nodes for
faster searching and enumeration:

```c
mxml_index_t *
mxmlIndexNew(mxml_node_t *node, const char *element,
             const char *attr);
```

The `element` and `attr` arguments control which elements are included in the
index.  If `element` is not `NULL` then only elements with the specified name
are added to the index.  Similarly, if `attr` is not `NULL` then only elements
containing the specified attribute are added to the index.  The nodes are sorted
in the index.

For example, the following code creates an index of all "id" values in an XML
document:

```c
mxml_index_t *ind = mxmlIndexNew(xml, NULL, "id");
```

Once the index is created, the [mxmlIndexFind](@@) function can be used to find a
matching node:

```c
mxml_node_t *
mxmlIndexFind(mxml_index_t *ind, const char *element,
              const char *value);
```

For example, the following code will find the element whose "id" string is "42":

```c
mxml_node_t *node = mxmlIndexFind(ind, NULL, "42");
```

Alternately, the [mxmlIndexReset](@@) and [mxmlIndexEnum](@@) functions can be used to
enumerate the nodes in the index:

```c
mxml_node_t *
mxmlIndexReset(mxml_index_t *ind);

mxml_node_t *
mxmlIndexEnum(mxml_index_t *ind);
```

Typically these functions will be used in a `for` loop:

```c
mxml_node_t *node;

for (node = mxmlIndexReset(ind);
     node != NULL;
     node = mxmlIndexEnum(ind))
{
  ... do something ...
}
```

The [mxmlIndexCount](@@) function returns the number of nodes in the index:

```c
size_t
mxmlIndexGetCount(mxml_index_t *ind);
```

Finally, the [mxmlIndexDelete](@@) function frees all memory associated with the
index:

```c
void
mxmlIndexDelete(mxml_index_t *ind);
```


Custom Data Types
=================

Mini-XML supports custom data types via per-thread load and save callbacks.
Only a single set of callbacks can be active at any time for the current thread,
however your callbacks can store additional information in order to support
multiple custom data types as needed.  The `MXML_TYPE_CUSTOM` node type
identifies custom data nodes.

The [mxmlGetCustom](@@) function retrieves the custom value pointer for a node.

```c
const void *
mxmlGetCustom(mxml_node_t *node);
```

Custom \(`MXML_TYPE_CUSTOM`) nodes are created using the [mxmlNewCustom](@@)
function or using a custom per-thread load callbacks specified using the
[mxmlSetCustomHandlers](@@) function:

```c
typedef void (*mxml_custom_destroy_cb_t)(void *);
typedef bool (*mxml_custom_load_cb_t)(mxml_node_t *, const char *);
typedef char *(*mxml_custom_save_cb_t)(mxml_node_t *);

mxml_node_t *
mxmlNewCustom(mxml_node_t *parent, void *data,
              mxml_custom_destroy_cb_t destroy);

int
mxmlSetCustom(mxml_node_t *node, void *data,
              mxml_custom_destroy_cb_t destroy);

void
mxmlSetCustomHandlers(mxml_custom_load_cb_t load,
                      mxml_custom_save_cb_t save);
```

The load callback receives a pointer to the current data node and a string of
opaque character data from the XML source with character entities converted to
the corresponding UTF-8 characters.  For example, if we wanted to support a
custom date/time type whose value is encoded as "yyyy-mm-ddThh:mm:ssZ" (ISO
format), the load callback would look like the following:

```c
typedef struct
{
  unsigned year,    /* Year */
           month,   /* Month */
           day,     /* Day */
           hour,    /* Hour */
           minute,  /* Minute */
           second;  /* Second */
  time_t   unix;    /* UNIX time */
} iso_date_time_t;

bool
load_custom(mxml_node_t *node, const char *data)
{
  iso_date_time_t *dt;
  struct tm tmdata;

 /*
  * Allocate data structure...
  */

  dt = calloc(1, sizeof(iso_date_time_t));

 /*
  * Try reading 6 unsigned integers from the data string...
  */

  if (sscanf(data, "%u-%u-%uT%u:%u:%uZ", &(dt->year),
             &(dt->month), &(dt->day), &(dt->hour),
             &(dt->minute), &(dt->second)) != 6)
  {
   /*
    * Unable to read numbers, free the data structure and
    * return an error...
    */

    free(dt);

    return (false);
  }

 /*
  * Range check values...
  */

  if (dt->month < 1 || dt->month > 12 ||
      dt->day < 1 || dt->day > 31 ||
      dt->hour < 0 || dt->hour > 23 ||
      dt->minute < 0 || dt->minute > 59 ||
      dt->second < 0 || dt->second > 60)
  {
   /*
    * Date information is out of range...
    */

    free(dt);

    return (false);
  }

 /*
  * Convert ISO time to UNIX time in seconds...
  */

  tmdata.tm_year = dt->year - 1900;
  tmdata.tm_mon  = dt->month - 1;
  tmdata.tm_day  = dt->day;
  tmdata.tm_hour = dt->hour;
  tmdata.tm_min  = dt->minute;
  tmdata.tm_sec  = dt->second;

  dt->unix = gmtime(&tmdata);

 /*
  * Assign custom node data and destroy (free) function
  * pointers...
  */

  mxmlSetCustom(node, data, free);

 /*
  * Return with no errors...
  */

  return (true);
}
```

The function itself can return `true` on success or `false` if it is unable to
decode the custom data or the data contains an error.  Custom data nodes contain
a `void` pointer to the allocated custom data for the node and a pointer to a
destructor function which will free the custom data when the node is deleted.
In this example, we use the standard `free` function since everything is
contained in a single calloc'd block.

The save callback receives the node pointer and returns an allocated string
containing the custom data value.  The following save callback could be used for
our ISO date/time type:

```c
char *
save_custom(mxml_node_t *node)
{
  char data[255];
  iso_date_time_t *dt;


  dt = (iso_date_time_t *)mxmlGetCustom(node);

  snprintf(data, sizeof(data),
           "%04u-%02u-%02uT%02u:%02u:%02uZ",
           dt->year, dt->month, dt->day, dt->hour,
           dt->minute, dt->second);

  return (strdup(data));
}
```

You register the callback functions using the [mxmlSetCustomCallbacks](@@)
function:

```c
mxmlSetCustomCallbacks(load_custom, save_custom);
```


SAX (Stream) Loading of Documents
=================================

Mini-XML supports an implementation of the Simple API for XML (SAX) which allows
you to load and process an XML document as a stream of nodes.  Aside from
allowing you to process XML documents of any size, the Mini-XML implementation
also allows you to retain portions of the document in memory for later
processing.

The mxmlLoadXxx functions support a SAX callback and associated data.  The
callback function receives the data pointer you supplied, the node, and an event
code and returns `true` to continue processing or `false` to stop:

```c
bool
sax_cb(void *cbdata, mxml_node_t *node,
       mxml_sax_event_t event)
{
  ... do something ...

  // Continue processing...
  return (true);
}
```

The event will be one of the following:

- `MXML_SAX_EVENT_CDATA`: CDATA was just read.
- `MXML_SAX_EVENT_COMMENT`: A comment was just read.
- `MXML_SAX_EVENT_DATA`: Data (integer, opaque, real, or text) was just read.
- `MXML_SAX_EVENT_DECLARATION`: A declaration was just read.
- `MXML_SAX_EVENT_DIRECTIVE`: A processing directive/instruction was just read.
- `MXML_SAX_EVENT_ELEMENT_CLOSE` - A close element was just read \(`</element>`)
- `MXML_SAX_EVENT_ELEMENT_OPEN` - An open element was just read \(`<element>`)

Elements are *released* after the close element is processed.  All other nodes
are released after they are processed.  The SAX callback can *retain* the node
using the [mxmlRetain](@@) function.  For example, the following SAX callback
will retain all nodes, effectively simulating a normal in-memory load:

```c
bool
sax_cb(void *cbdata, mxml_node_t *node, mxml_sax_event_t event)
{
  if (event != MXML_SAX_ELEMENT_CLOSE)
    mxmlRetain(node);

  return (true);
}
```

More typically the SAX callback will only retain a small portion of the document
that is needed for post-processing.  For example, the following SAX callback
will retain the title and headings in an XHTML file.  It also retains the
(parent) elements like `<html>`, `<head>`, and `<body>`, and processing
directives like  `<?xml ... ?>` and declarations like `<!DOCTYPE ... >`:

```c
bool
sax_cb(void *cbdata, mxml_node_t *node,
       mxml_sax_event_t event)
{
  if (event == MXML_SAX_ELEMENT_OPEN)
  {
   /*
    * Retain headings and titles...
    */

    const char *element = mxmlGetElement(node);

    if (!strcmp(element, "html") ||
        !strcmp(element, "head") ||
        !strcmp(element, "title") ||
        !strcmp(element, "body") ||
        !strcmp(element, "h1") ||
        !strcmp(element, "h2") ||
        !strcmp(element, "h3") ||
        !strcmp(element, "h4") ||
        !strcmp(element, "h5") ||
        !strcmp(element, "h6"))
      mxmlRetain(node);
  }
  else if (event == MXML_SAX_DECLARATION)
    mxmlRetain(node);
  else if (event == MXML_SAX_DIRECTIVE)
    mxmlRetain(node);
  else if (event == MXML_SAX_DATA)
  {
    if (mxmlGetRefCount(mxmlGetParent(node)) > 1)
    {
     /*
      * If the parent was retained, then retain this data
      * node as well.
      */

      mxmlRetain(node);
    }
  }

  return (true);
}
```

The resulting skeleton document tree can then be searched just like one loaded
without the SAX callback function.  For example, a filter that reads an XHTML
document from stdin and then shows the title and headings in the document would
look like:

```c
mxml_node_t *doc, *title, *body, *heading;

doc = mxmlLoadFd(/*top*/NULL, /*fd*/0,
                 /*load_cb*/NULL, /*load_cbdata*/NULL,
                 sax_cb, /*sax_cbdata*/NULL);

title = mxmlFindElement(doc, doc, "title", NULL, NULL,
                        MXML_DESCEND_ALL);

if (title)
  print_children(title);

body = mxmlFindElement(doc, doc, "body", NULL, NULL,
                       MXML_DESCEND_ALL);

if (body)
{
  for (heading = mxmlGetFirstChild(body);
       heading;
       heading = mxmlGetNextSibling(heading))
    print_children(heading);
}
```

The `print_children` function is:

```c
void
print_children(mxml_node_t *parent)
{
  mxml_node_t *node;
  const char *text;
  bool whitespace;

  for (node = mxmlGetFirstChild(parent);
       node != NULL;
       node = mxmlGetNextSibling(node))
  {
    text = mxmlGetText(node, &whitespace);

    if (whitespace)
      putchar(' ');

    fputs(text, stdout);
  }

  putchar('\n');
}
```


Migrating from Mini-XML v3.x
============================

The following incompatible API changes were made in Mini-XML v4.0:

- SAX events are now named `MXML_SAX_EVENT_foo` instead of `MXML_SAX_foo`.
- SAX callbacks now return a boolean value.
- The mxmlSAXLoadXxx functions have been removed in favor of passing the SAX
  callback function and data pointers to the mxmlLoadXxx functions.
- Node types are now named `MXML_TYPE_foo` instead of `MXML_foo`.
- Descend values are now normalized to `MXML_DESCEND_ALL`, `MXML_DESCEND_FIRST`,
  and `MXML_DESCEND_NONE`.
- Functions that returned `0` on success and `-1` on error now return `true` on
  success and `false` on error.
- CDATA nodes ("`<![CDATA[...]]>`") now have their own type (`MXML_TYPE_CDATA`).
- Comment nodes ("`<!-- ... -->`") now have their own type
  (`MXML_TYPE_COMMENT`).
- Custom node callbacks are now set using the [mxmlSetCustomCallbacks](@@)
  function instead of mxmlSetCustomHandlers.
- Declaration nodes ("`<!...>`") now have their own type
  (`MXML_TYPE_DECLARATION`).
- Element attributes are now cleared with the [mxmlElementClearAttr](@@)
  function instead of mxmlElementDeleteAttr.
- Processing instruction/directive nodes ("`<?...?>`") now have their own type
  (`MXML_TYPE_DIRECTIVE`).
- Integer nodes (`MXML_TYPE_INTEGER`) now use the `long` type.
- Text nodes (`MXML_TYPE_TEXT`) now use the `bool` type for the whitespace
  value.