xattrs field names restriction and undocumented error codes

While trying to upsert docs to xattrs, I am hitting into errors as below : 

Error mutating document doc945 : Invalid extended attribute (0x87) | {"status_code":135,"document_id":"doc945","bucket":"b1","scope":"s1","collection":"c1","collection_id":12,"error_name":"XATTR_EINVAL","error_description":"Invalid extended attribute","opaque":1008,"context":"Request XATTR key invalid","last_dispatched_to":"172.23.106.130:11210","last_dispatched_from":"172.16.2.78:57652","last_connection_id":"35fdea16e35a6a45/4c0e446a21005348"} Retrying 

So when tried to query the error code 135, its not present in Couchbase Docs
The last error code for this xattr feature present in docs is 130 and I am getting 135.

With trial and error, it was found that the xattrs field names has limit of max 15 characters.

so, field name : vector_data_base64 (18 > 15 ) is invalid ( returning the above error ) but, field name : vector_encoded is valid.

So there are two concerns here,

1. The field character limit of 15 characters seems too less ( in normal doc we don't have any such limits ). 
eg. for upserting base64 vecs to xattrs, one of the ideal names is vector_data_base64 but this will return error.

2. Also, if the character limit still exists, then this needs to be documented.