re_highlight() adds the conditional formatting of highlighted vectors in
... to a highlighted or un-highlighted vector x.
The primary function of re_highlight() is to restore the format method of a
highlighted vector after un-highlighting it during an intermediate operation.
See the Highlight, Un-Highlight, Re-Highlight section of
vignette("vlightr") for more details.
re_highlight(un_highlight(x_hl), x_hl) and x_hl are equivalent for a
highlighted vector x_hl.
re_highlight() and rl() are synonyms.