A character assigned to UCNMCHAR must not be a LC Letter, UC Letter, Digit, RE, RS, SPACE or SEPCHAR, nor can it be a LCNMSTRT or UCNMSTRT.

#0060   Markup Error

ISO 8879, 13.4.5

A character assigned to UCNMCHAR must not be a LC Letter, UC Letter, Digit, RE, RS, SPACE or SEPCHAR, nor can it be a LCNMSTRT or UCNMSTRT.