Nested brackets

• PROT[mod:Fe[III]]EOFORM
  Nested brackets need to considered for the fairly common case that they are within descriptors.

Unclosed brackets

• PROT[info:jk :] lol]EOFORM
  I don't think handling unclosed brackets is worth it, so I'd suggest throwing parsing and writing errors if the number of [ doesn't match that of ].

Back-to-back unclosed brackets

• PROT[info:jk :] [: lol]EOFORM
• PROT[info:unclosed][brackets]EOFORM
• PROT[info:Unclosed]B[rackets]EOFORM
  These are wacky, considering back-to-back unclosed brackets within descriptors. These will lead to unexpected behavior because we assume closed brackets are tags. We should consider making a writer exception if the user tries to write these types of unclosed brackets in descriptors.