NODE_ID_RE

Matches a node id as the compiler emits it: lower case, with dots, dashes and underscores allowed, and — for an id a @define template declares — the hygienic suffix ~<n> (D36). Inside a template the compiler writes a text reference in that emitted form too (D59), so of: #density arrives as #density~2; the suffix is opaque and the whole string is the id.