XML is a mainstream approach providing semantics for science, such as MathML, SBML/BIOPAX (biology), GML and KML (geo) SVG (graphics) and NLM-DTD, ODT and OOXML (documents). CML provides support for most chemistry, especially molecules, compounds, reactions, spectra, crystals and computational chemistry (compchem)...
CML has been developed by Peter Murray-Rust and Henry Rzepa since 1995. It is the de facto XML for chemistry, accepted by publishers and with more than 1 million lines of Open Source code supporting it. CML can be validated and built into authoring tools (for example the Chemistry Add-in for Microsoft Word). A list of CML-compliant and CML-aware software can be found on the software page.