The coordinate system definition file can define textual notes associated with each coordinate system, reference frame, and with conversions between them. This can include notes about coordinate systems not defined in the file (for example explaining why they are not defined), and about conversions that are not possible (explaining why not).
These are defined in sections
[reference_frame_notes] reference frame notes [coordinate_system_notes] coordinate system notes
Within each section the notes are organised as:
code1 code2 code3... First line of notes Second line of notes ... end_note
The first line of each note defines the coordinate systems or reference frames that the note applies to. It can also define conversion between coordinate systems or reference frames as code1:code2. This will apply for transformations from system code1 to code2. It will also apply to the reverse transformation, unless a note is explicitly defined for it.
The codes line is followed by the text of the note, which may use as many lines as required, and then a final line with just the text "end_note".