Different file types can change the behaviour of Bluefish. File types are recognized by their extension, or by the beginning of the file's contents. The current document type is shown in the far right of the status bar. If the type of a file is not properly detected, you can change the type using the → menu. See Chapter VIII, Customising Bluefish to change these extensions.
Syntax highlighting is the coloring of words that have special meaning for a language. The patterns can vary: for example, "<title>" means "start of title" in HTML, "function" means "start of function" in PHP.
While editing, Bluefish will only update the highlighting patterns in the block of text around the cursor. The number of lines (the size) of this block can be adjusted in the preferences under Editor. The syntax highlighting for the total document can be refreshed using the → (F5) menu. It can be disabled in the preferences under Editor. For more information about adding or modifying syntax highlighting for existent or new languages, see here.