The internal editor that Kile uses is Kate. Kate is a text editor created for programmers, which incorporates the ability to read and highlight many different types of text files, among which L^AT_EX and BibT_EX; you can access many options for Kate directly from the Kile Tools menu.

To learn more about Kate and its capabilities, see the Kate Handbook. Kile users can start reading from the chapter “Working with the Kate Editor”.