type MatteMode = "Alpha" | "AlphaInverted" | "Luma" | "LumaInverted";Experimental
The channel of a matte source that masks a block. Experimental: this API may change in a minor release.
'Alpha': the block shows where the source is opaque.'AlphaInverted': the block shows where the source is transparent.'Luma': the block shows where the source is bright.'LumaInverted': the block shows where the source is dark or transparent.