Lexer - is a configuration of lexis analysis component. It is a resource, it is not a separate code implementation.
No programming is required to make syntax highlighting for new text file format.
Lexis analysis is based on the syntax rules. There are three type of rules:
Styles is used to define text drawing parameters. It is possible multiple styles will be applied to a portion of text. Style merging procedure specifies sequence in which styles are merged into canvas parameters.
Lexer library - is a collection of lexers. It allows to automate file extension managing for selecting appropriate lexer, constructing filter for open | save dialogs, open/save lexers into single file.
If you use nested lexers it's recommended to include master and slave lexers into lexer library.