630 Subfield $x - General subdivision:

Subfield $x contains a subject subdivision that is not more appropriately contained in subfields $v (Form subdivision) , $y (Chronological subdivision) , or $z (Geographic subdivision) . Subfield $x is appropriate only when a general topical subdivision is added to a uniform title.

Examples:

630 00$aBeowulf$xLanguage$vGlossaries, etc.

630 00$aTalmud$xTheology.