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:

• Token rules are intended to extract tokens from the text
• Token block rules (block rules) are intended to find text ranges (group of tokens), line separators and key words detection
• Sub lexer rules are intended to define regions where nested lexers will act.

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.