> <\body> serialization> Users may write their own extensions to in the extension language. In that context, trees are usually represented by expressions. The syntax was designed to be predictable, easy to hand-edit, and expose the complete internal structure of the document. For instance, the formula () is represented by <\tm-fragment> The representation may also be useful in order to represent complex macros with a lot of programatic content. Finally, is the safest format when incorporating snippets into emails. Indeed, both the standard format and the XML serialization may be quite sensitive to white-space. In order to save or load a document in format, you may use . Files saved in format can easily be processed by external programs, in the same way as files saved in XML format can easily be processed by tools for processing XML, like XSLT. In order to copy a document fragment to an email in format, you may use . Similarly, you may paste external fragments into using . The format may also used interactively inside sessions or interactive commands. For instance, typing followed by the interactive command <\scm-code> (insert '(frac "1" "2")) inserts the fraction at the current cursor position. >