More information about Unified Standard Format Markers (USFM) is available from the official USFM information.
Bibledit supports several of the markers.
By editing the stylesheet of a project, the number of supported markers can be extended. Completely new markers can be added too, but this is not recommended. It is recommended to stick to the USFM standard. A style can be edited by opening a stylesheet, then switching the Edit mode on, and then editing that style.