Determining glyph availability for FOP

I've just spent the past hour grappling with getting FOP to render the Unicode glyph for a checkmark (U+2713) in PDF output from XSL:FO. I thought I'd share a few things I learnt along the way (that make me feel a bit silly for not knowing them already).

The type of errors I was getting were:

Glyph "✓" (0x2713, checkmark) not available in font "Times-Roman".

Some observations after messing around for far too long:

1. Fop does not support fallback to a secondary font on a character-by-character basis. If you need a glyph to be rendered that isn't present in your font, well, bad luck. (Unless you specifically tweak your XSL:FO document, which isn't viable in my case.)
2. There is no way, as far as I can see, that you can map a specific character to use a different font.
3. There is a great resource at fileformat.info that will tell you what fonts support your glyphs.
4. Just use DejaVu Sans and save yourself a lot of tweaking.

Determining glyph availability for FOP was originally published by Martin Paul Eve at eve.gd: Martin Paul Eve on July 28, 2013.