The ANSI Highlighter

ANSI SGR Codes

The ANSI Highlighter (that is, the Rexx Highlighter operating in ANSI mode) uses ANSI SGR (Select Graphic Rendition) codes to highlight a Rexx program. Only a subset of all the ANSI SGR codes are used, namely (ESC denotes character "1B"X):

Different SGR codes can be combined in a single sequence by separating them using semicolons. For example, ESC[1;3;38;2;255;0;0m means "choose a bold font, choose an italic font, and set the foreground color to pure red".

Implementation differences

Terminal applications and emulators differ wildly in their support of ANSI SGR codes. The default configuration of the Windows terminal, for example, implements boldface by substituting colors with a lighter version of themselves, and that, only for basic colors (i.e., codes 30-37, 40-47, 90-97 and 100-107); the same is true of the default terminal for Ubuntu WSL.

Additionally, support for basic colors is abundantly erratic: see, as an example, the color chart that appears in the Wikipedia. In an attempt to minimize this problem, all the colors generated by the ANSI highlighter are emitted using the 38 and 48 codes, i.e., they are pure RGB colors. CSS named colors are also translated to their RGB definitions: you can be sure that foreground blue will be generated as #0000ff, that is, as ESC[38;2;0;0;255m. How this displays in your emulator may vary.

Please note that some less known terminal emulators, like Sakura, seem to work much better, out of the box, than the standard Windows tools.

Selecting ANSI mode

If you are working from the command line, the highlight utility will automatically select ANSI mode when attempting to highlight a .rex program. You can also manually select ANSI mode by using the -a or --ansi options.