Field-level CustomData: what is there, and does a bare string survive a round trip?

document 55643   pages 3

wrote a BARE-STRING marker onto TEXT.1.0
   signHere:721E1:56198;H=55;L=190;T=1229;W=229;oimg=objImg_ABC1234
   in memory reads back: signHere:721E1:56198;H=55;L=190;T=1229;W=229;oimg=objImg_ABC1234
saved.

after a fresh LoadDocument: HELD
   signHere:721E1:56198;H=55;L=190;T=1229;W=229;oimg=objImg_ABC1234

So a field CAN hold a non-JSON CustomData server-side, and the #110 hazard is real:
JObject.Parse throws on this and the old catch replaced it with {}.

FieldStash.TryOpen (the #110 guard) against real values:
   signHere:721E1:56198;H=55;L=190;T=1229;W=229;oimg=objImg_ABC1234 -> REFUSED: carries a signature marker
   {"sdFontOrig":24}                                    -> may stash
   {"signHereId":"C51382A","instanceId":"9E9EB"}        -> REFUSED: carries a signature marker
   [1,2,3]                                              -> REFUSED: custom data is in another format
   not json at all                                      -> REFUSED: custom data is in another format
                                                        -> may stash

cleaned up: deleted document 55643