Accessing _UseClipRect in the Shader

Since the new 2D Rect Mask is using MaterialPropertyBlocks internally, is there a way to determine whether or not _UseClipRect is set to 0 or 1?

Could you elaborate what you mean? This value is set to either 0 or 1 depending on if the rect should be used.

When I try to get that value from the shader, it is always 0 even though it is clearly set to 1 (somewhere) and executed correctly by the shader. Unless I am missing something, I am thinking it might be due to that property being set by the materialpropertyblock.

In the end, I am just trying to get the value of _UseClipRect to know if it is set to 0 or 1.