Filter Name

Name is displayed in filter list in open and save dialog.

Help File

Enter path to help file, local or web address. Allows the variable %word% as part of the path, where %word% shall be replaces with the current word. Once path is set, you may press Alt+F1 to display associated help for actual word (e.g. if you edit HTML code and cursor is on the "body" word, after Alt+F1 help for HTML syntax is opened and you will see context for "body" keyword). In Multi-Highlighter, the called help depends on the part of code you are in.

File Masks

With this setting, you choose which highlighter will be active when you open this file type. In Filter Name of HTML Document, you find File Masks of *.htm and *.html. That means any files you open in PSPad with those extensions will use this highlighter.

Tab Width

You can define your own highlighters. If you use one of the bolded highlighters (bold in highlighter list), list of user definition is enabled, last five (5). Now you can clicking on items in list assign highlighter definition to one of three user highlighter position.
In this case are filter name and file masks taken from user highlighter definition. See User highlighters.

Extended Indent Chars

Some program languages (PHP, C,...) uses indentation for code writing:
xxx {
  xxx {

You can define chars for extended indentation.