15.3.4.13 Primitive syntactic bindings: fluid syntaxes

A syntactic binding representing a fluid syntax defined by the boot image has descriptor with format:

($fluid . ?fluid-label)

where ?fluid-label is a further label gensym used to redefine the keyword binding; How fluid syntaxes work.

Some of the fluid syntaxes are: __who__, return, continue, break, with, brace, <>.