A text based format that originated in the early days of the internet, and was mainly used in news groups to exchange chords. It usually has one of the following file extensions: pro, chopro, chordpro, cpm, and occasionally txt or crd, though the later usually refers to regular text chords.
(Note: by "text based" i mean plain text, as in files created in Notepad on windows or TextEdit on a mac. There are of course many such editors, which might be better for some, and allow for more advanced options, like notepad++ on windows, or Text Wrangler on mac)
Chords are written in brackets, "[]", in-line with the lyrics at the position that chords are to be played. In example:
A[G]lways l[Em]ook on the l[Am]ight s[D7]ide of l[G]ife
would result in:
G Em Am D7 G
Always look on the light side of life
The rest of the format is based on lines containing commands in curled brackets, "{}", and lines containing invisible comments that start with a number sign, "#". The following table contains the different available commands which are the most common commands used (there are more commands which were originated from the different implementations of the format):