A markup language used to express chemical information. CML is an extension of XML (extensible markup language), which is widely used to store and transfer text. A particular feature of XML is the use of tags to identify different types of information. These are commonly in angle brackets. In the text version of this dictionary, for example, headwords are surrounded by the tags <hw>…</hw>, cross references are identified by <xr>…</xr>, etc. In CML, there are tags for many different types of chemical information. For example, structures can be represented by tagged data giving the atoms and their coordinates in two or three dimensions. Reactions can also be indicated, as well as data for spectra and other properties.
http://www.ch.ic.ac.uk/rzepa/chimeral/documents/FAQ/FAQ.html An FAQ produced by the Chemistry Department, Cambridge University