regularstring = /((\\\v)|(\\\f)|(\\\a)|(\\\r)|(\\\b)|(\\\t)|(\\\n)|(\\\{)|(\\\})|(\\\~)|(\\\\)|([^~{}\\]))*/

unq_document: unq_string
unq_document:

substring: regularstring
substring: substring regularstring ? concat_strings

unq_tag: '{' unq_string '}' ? anon_tag
unq_tag: '~' regularstring '{' unq_string '}' ? named_tag
unq_tag: '{' '}' ? empty_anon_tag
unq_tag: '~' regularstring '{' '}' ? empty_named_tag

unq_string: substring ? simple_anon_tag
unq_string: unq_tag
unq_string: unq_string substring ? concat_ustring_string
unq_string: unq_string unq_tag