Scintilla is a free source code editing component. It comes with
complete source code and a license that permits use in any free project
or commercial product.

As well as features found in standard text editing components,
Scintilla includes features especially useful when editing and
debugging source code. These include support for syntax styling, error
indicators, code completion and call tips. The selection margin can
contain markers like those used in debuggers to indicate breakpoints
and the current line. Styling choices are more open than with many
editors, allowing the use of proportional fonts, bold and italics,
multiple foreground and background colours and multiple fonts.