首楞嚴義疏注經 8.198

8.198

如故即一切法，真故離一切相。此真如體亦不可得，故云二無所著。亦即三諦，對文可見。此菩薩了一切法即真法界，無相可離，名為如相。

Being "suchness" (tathā), it is identical to all dharmas; being "true" (satya), it is free from all characteristics. The substance of this tathatā is also unattainable, hence it says "no attachment to either." It also denotes the three truths, as can be seen against the text. This bodhisattva thoroughly understands that all dharmas are just the true dharmadhātu, with no characteristics to be freed from; this is called the character of suchness.