XML.

About XML.
Converting between schema formants.
relaxng-mode.
utilities for processing xml.
Microformats.
XML encoding.
Validation of xml files.

Converting between schema formants.

$ man trang
trang [-I rng|rnc|dtd|xml] [-O rng|rnc|dtd|xsd] $input $output

See:

http://code.google.com/p/xsdtorngconverter/: That XSLT transformation converts a XSD schema to RelaxNG.

relaxng-mode.

http://www.pantor.com/download.html: RNC Emacs Mode (home page)
http://www.emacswiki.org/emacs/RELAX_NG: Emacs wili.
http://www.relaxng.org/compact-tutorial-20030326.html: relaxng compact syntax tutorial

XMLStarlet is a set of command line utilities (tools) which can be used to transform, query, validate, and edit XML documents and files using simple set of shell commands in similar way it is done for plain text files using UNIX grep, sed, awk, diff, patch, join, etc.

http://xmlstar.sourceforge.net/overview.php: home page

Cygwin.

cmd# setup.exe -p libxml2,libxslt

libxslt provide xsltproc, libxml2 provide xmlcatalog and xmllint.

XPath query from CLI.

$ xmllint --xpath $XPATH file.xml

Microformats.

http://microformats.org/about

XML encoding.

http://www.ietf.org/rfc/rfc3023.txt: XML Media Types
http://www.xml.com/pub/a/2004/07/21/dive.html: XML on the Web Has Failed

Validation of xml files.

$ jing schema.rng in.xml
$ xmllint --relaxng schema.rng in.xml

See:

http://infohost.nmt.edu/tcc/help/xml/lint.html: xmllint: A validator for XML files
http://www.cogsci.ed.ac.uk/~richard/rxp.html: RXP - an XML parser available under the GPL

Validating using the DOCTYPE.

$ xmllint --valid --noout file.xml

Validating against a specific DTD.

$ xmllint --noout --dtdvalid URL file.xml

Validating against a Relax NG schema.

$ xmllint --noout --relaxng schema.rng file.xml

If your schema is in Compact Format, you can use the trang program to convert it to RNG format:

$ trang file.rnc file.rng

Validating against XSchema.

$ xmllint --noout --schema schema.xsd file.xml