custom data field

[chad-earthscope]

Submitted by @andreas-wuestefeld

Experience with many other formats is that during conception of the format it is never fully anticipated how it is going to be used.

Often, pre-defined header fields are canabalized for other purposes (notably in SEGY...)
I would suggest to add an empty container that can be used for custom (non-standard) header information where people could write things like VSP charge, or moment tensors, or weather conditions...