🚀 go-pugleaf

I'm not very clear about using glyphs, and I hope somone
would be kind enough to answer the following questions:

1) I understand that in Glyph::allocate(Canvas*, const Allocation& allocation,
	Extensions& extension), the allocation informs the glyph how much
	space has been allocated. But what is the purpose of the
	extension? This was never explained.

2) I wish to write dynamic glyphs that change their
appearances as data is read from a file.
Is it safe to save the Canvas and the allocation passed in Glyph::allocate() 
for use in drawing operations?

Thanks for any help.

Mike