meaning of $ in tablegen

What is the meaning of a $ sign in tablgen? Here is an example

// Pattern fragments
def vextract_sext_i8 : PatFrag<(ops node:$vec, node:$idx),
(MipsVExtractSExt node:$vec, node:$idx, i8)>;


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Taken from

Whenever you use a variable in TableGen, you write it


The name is always prefixed with a $, similar to how in IR, identifiers are always prefixed with % or @.