What is "SourceTo" input in Transform Node (transform)

What is the SourceTo input on the "Transform (transform)" node?

I am unable to find in TFM for Fusion, or the forum, anything about the (transform) node, explicitly (and I have mostly read the chapter 58 on Transform Nodes). If anything, the manual says "two inputs: effect mask and input", but nothing about SourceTo (or at least SourceTo is not searchable in the pdf).

thanks.

That is the OpenFX Transform from the Edit page. The Fusion Transform has XF after it if you hover over it.

Thanks @xunile. Makes sense now why I can't find it in the manual. So I can assume from now on, anything not in the manual is OpenFX instead of native BMD effects. That said, I looked back on the edit page at the OpenFX transform, and I can't seen anything about SourceTo. Looked on the OpenFX page too and I couldn't find anything there. I guess I need never know what it does and will switch to using Transform (Xf).

It seems like the SourceTo input allows you to connect a second piece of media which the controls of the node then act on, merging it with the original source. You can then use the Composite Type control to blend the two inputs.