There is nothing like a special library format. The ones that have been
introduced in 1.4.1 just use some nice (and time consuming) features of GNU
m4. The only predefined format is the one of the contents file
which is read during startup. It is made up of two basic line types:
menu entry = "TYPE="name
contents line = template":"package":"value":"description
name = String
template = String
package = String
value = String
description = String
String = <anything except ":", "\n" and "\r">
No leading white spaces or comments are allowed in this file. If you need either one, define a command that removes them before loading. Have a look to the libraryContentsCommand resource.
The menu entry will appear in the selection menu at the top and of the library window.