The reason is that XML software should be small, fast, and compatible.
HTML browsers are allowed to display HTML documents with errors (like missing end tags). A "well formed" XML document is not the same as a "valid" XML document. In addition, it must conform to a document type definition.
As an event-based, non-validating XML parser, Expat is fast and small, and a perfect match for PHP web applications. The risk from using it lies entirely with the user.
Such changes are not needed in xmltex as the input syntax is always XML.
Some language files may change the meaning of such characters as install file and produce a `cut down' latex that did not have features that are not going to be used in xmltex.
Unfortunately the support for this method of building xmltex (and access to non English hyphenation generally) is not fully designed and totally undocumented.
xmltex by default `knows' nothing about any particular type of XML file, and so needs to load external files containing specific information.
If you want to learn more about XML, please visit our XML tutorial. Event-based parsers focus on the content of the XML documents, not their structure.
However, the example is not valid XML, because there is no Document Type Definition (DTD) associated with it.
In addition to the `catalogue' commands described earlier there are other commands that may be placed in the configuration files.
may be used in the input path of `normal' Te X, this will then be used for additional information loaded each run.
Normally however the information from the parse is used to trigger Te X typesetting code.