080 Subfield $x - Common auxiliary subdivision:

Subfield $x contains a common auxiliary subdivision, a number that qualifies the concept represented by the main UDC number. Common auxiliary subdivisions, such as those for form (e.g., dictionaries), are attached to a main UDC number preceded or delimited by some kind of facet indicator. Examples of commonly used subdivision delimiters are parentheses, brackets, an apostrophe, or a hyphen.

Examples:

080 ##$a821.113.1$x(494)$2[edition information]

080 ##$a94$x(474)$x"19"$x(075)$2[edition information]