URI
Notation
[]
Caption
Subgrouping (square brackets). Table 1b
Scope Note
Square brackets [ ] may be used as a subgrouping device within a complex combination of UDC numbers, in order to clarify the relationship of the components. Subgrouping may be needed when a subject denoted by two or more UDC numbers linked by plus sign, stroke or colon is as a whole related to another number by colon, or is modified by a common or special auxiliary
Examples
[622+669](485) Mining and metallurgy in Sweden
Broader class
--  COMMON AUXILIARY SIGNS