On 04/09/2016 03:46 PM, Eli Zaretskii wrote:
> The default fontset already defines specific blocks to be handled by
> these fonts, see fontset.el.  What problems, specifically, do you have
> with the default setup and the current emacs-25 branch?

I get relatively inconsistent results in terms of which font is chosen to display a given symbol. The pair of fonts that I mentioned (Ubuntu Mono and Symbola) was just an example; my question is about configuring fallbacks for any given pair of fonts: it could be Source Code Pro and Asana Math instead of Ubuntu Mono and Symbola, for example.

>> What's the proper way to configure font fallback?
> 
> In general: find the characters you want to change and augment the
> default fontset to use the font you want for them.

Is it enough to augment the default fontset? Changing the :height of the 'default font creates a new fontset, which doesn't respect the fallbacks that I configure. Hence my using

  (dolist (ft (fontset-list))
    (set-fontset-font ft 'unicode (font-spec :name "Ubuntu Mono"))
    (set-fontset-font ft 'unicode (font-spec :name "Symbola") nil 'append))

> But let's first see the specific problems you have with the Emacs 25
> defaults.  This issue got some attention a few months ago, so I'm
> surprised to hear there are still problems in that area.
> 
>> *Note*: for testing purposes, here are a few math characters: `ℕ𝓟⧺×≠≥≤±¬∨∧∃∀λ⟿⟹⊥⊤⊢`
> 
> Which, if any, of those give you trouble with the default fontset?

𝓟 is displayed using `Latin Modern Math' in emacs -Q, it seems. In any case, Ubuntu Mono and Symbola were just two examples.