I mean -- the thing is, I don't think canon will introduce any other realms than those two, so I think it boils down to interpretation. Wiki says: "Unlike bile sacs, glyphs do not contain their own magic; rather, they command the natural magic on the Boiling Isles, rendering them useless in any realm with no magic." It really could go either way, I think.
The way they work is: you draw the thing, you tap dat, and boom -- magic. So I guess my main concern here is that if they work and other characters can learn it, it would come down to introducing an entire new way of doing magic to the world. OTOH, it is pretty limited so far -- known glyphs at Eda's canon point are light, ice, fire, plants and invisibility (which only works as long as the caster holds their breath). Those things can do some real damage if applied right, though; bigger glyphs result in bigger magic, so e.g. a big light glyph will make a big ball of light, a big ice glyph will make a big ice pillar etc.
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The way they work is: you draw the thing, you tap dat, and boom -- magic. So I guess my main concern here is that if they work and other characters can learn it, it would come down to introducing an entire new way of doing magic to the world. OTOH, it is pretty limited so far -- known glyphs at Eda's canon point are light, ice, fire, plants and invisibility (which only works as long as the caster holds their breath). Those things can do some real damage if applied right, though; bigger glyphs result in bigger magic, so e.g. a big light glyph will make a big ball of light, a big ice glyph will make a big ice pillar etc.