CML - Chemical Markup Language File is a file extension that is suitable for specifying chemical information. You will be able to use this extension when it comes to finding descriptions of different molecules as well. You will also be able to find out molecule structures and much more. It is also used for exchanging and even archiving chemical data. It comes in handy when you need it the most. There have also been various versions that have been developed since the first one came out. There is also a very strict DTD specification you will be able to use when it comes to the CML language.