align-highlight-rule is an interactive autoloaded compiled Lisp function in `align.el'.

(align-highlight-rule BEG END TITLE &optional RULES EXCLUDE-RULES)

Highlight the whitespace which a given rule would have modified.
BEG and END mark the extent of the region. TITLE identifies the rule
that should be highlighted. If RULES or EXCLUDE-RULES is set to a
list of rules (see `align-rules-list'), it can be used to override the
default alignment rules that would have been used to identify the text
to be colored.