Referencing other subsets

Unicode regular expressions cannot reference collections defined in ISO/IEC 10646. Likewise, they cannot reference other regular expressions. Thus, regular expressions cannot directly capture collections defined in terms of other collections. It is thus necessary to create a gigantic regular expression by copying the definition of each referenced collection. This might be acceptable for MODERN EUROPEAN SCRIPTS (collection 283). But it is too inconvenient for COMMON JAPANESE (collection 287) since it references JIS2004 IDEOGRAPHICS EXTENSION (collection 371), which contains 3695 code points.