def validate_identifier(self, field):
if field.data:<EOL><INDENT>field.data = field.data.lower()<EOL>if Community.get(field.data, with_deleted=True):<EOL><INDENT>raise validators.ValidationError(<EOL>_('<STR_LIT>'<EOL>'<STR_LIT>'))<EOL><DEDENT><DEDENT>
Validate field identifier.