Re: font-lock as a single command

[Christopher Dimech]

> Sent: Saturday, February 13, 2021 at 12:08 PM
> From: "Emanuel Berg via Users list for the GNU Emacs text editor" 
> <help-gnu-emacs@gnu.org>
> To: help-gnu-emacs@gnu.org
> Subject: Re: font-lock as a single command
>
> Christopher Dimech wrote:
> 
> > (font-lock-add-keywords MODE KEYWORDS &optional HOW)
> >
> > What does the optional HOW actually do?
> 
> It is actually described in the docstring:
> 
>   If optional argument HOW is ‘set’, they are used to replace
>   the current highlighting list. If HOW is any other non-nil
>   value, they are added at the end of the current
>   highlighting list.

I understood none of that.  What is "replace the current highlighting list"
about?
 
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> underground experts united
> http://user.it.uu.se/~embe8573
> https://dataswamp.org/~incal
> 
> 
>