成唯識論述記 8.475

8.475

述曰：容起染故，假說通染，非體染故，名為染也。餘通二種者，謂行及有，行通善染，有亦通無記故。

The Commentary states: Because defilement may arise, they are metaphorically said to encompass defilement; they are not named defiled because their substance is defiled. 'The remaining encompass both kinds' refers to formations and existence, because formations encompass the wholesome and defiled, and existence also encompasses the indeterminate.