What is a 'decorated sequence'?

A decorated sequence has two parts: the sequence (the elements) and the decoration (the value). In Pattern<V>, the elements are the sequence and the value is the decoration.

The general Gram notation form makes this visible:

["decoration" | element1, element2, element3]

The string "decoration" is the value. element1, element2, element3 are the elements — each itself a pattern. The vertical bar separates decoration from sequence.

This framing is more accurate than calling Pattern<V> a node, a tree, or a record. A node suggests graph membership. A tree suggests a parent-child hierarchy with a root. A record suggests a flat bag of named fields. None of these captures what Pattern<V> actually is.

A decorated sequence captures: here is a value, and here are the ordered sub-things it is made of or relates to. What those sub-things mean — graph elements, lines of a poem, nested JSON arrays — is determined by how you interpret the pattern, not by the pattern itself.