XS_VALID_CHARS_FOR_REBAR_SUB_ID_WITH_LETTERS
Category in Advanced options dialog: Numbering
Use this advanced option to specify the valid letters for the reinforcing bar identifiers when they are shown by SUB_ID_WITH_LETTERS. Enter all the valid letters, for example, ABEG. By default, letters A–Z are valid.
This advanced option is model specific and the setting is saved in the options database.