Editing Vile (text editor) (section)

===Syntax highlighting===
vile performs syntax highlighting by running a ''syntax filter'' program which parses the buffer contents.  Initially this was a separate program.  However, to improve performance and avoid display problems, these syntax filters usually are compiled into the editor.  Most of the syntax filters are implemented with [[lex programming tool|lex]] (preferably [[Flex lexical analyser|flex]]), with the remainder in [[C (programming language)|C]] to address irregular grammars such as [[Perl]] and [[Ruby (programming language)|Ruby]].  All of the syntax filters follow the same design:
* Read from an external file the color- and video-attribute information into a [[hash table|chained hash table]],
* Parse the file according to the [[lexical rule]]s,
* Find the corresponding color- and video-attribute information for each lexical element, and
* Write a [[Markup language|marked-up]] copy of the file which is read by vile (via a pipe if the syntax filters are external programs, or via a function call if they are internal).

vile paints the markup information on top of the buffer contents using in regions delimited by line and column numbers.  The markup is not attached to the underlying buffer contents.  To update the markup as the buffer is changed requires reanalysis.  This is done automatically when the user pauses.