The assumption is that fonts with PostScript outlines (Type 1 or OpenType CFF/.otf) will have a 1000-unit em, and fonts with TrueType outlines, a 2048-unit em. What is considered “standard” is dependent on the outline format.Hrant H. Papazian said:Unless you have a good reason to not use 1000, use 1000, since some software still assumes it.
Lowercase being more legible than uppercase can also be explained by the letter shapes being, individually, more distinctive. The question has been specifically investigated, btw—the exact way you are asking it above. Came to the conclusion that word shape was not contributing much.John Savard said:
Obviously, the individual letters must be important; if one takes a sample of English text, and blurs it so that only the bouma is visible, it becomes unreadable. But it's also true that lower-case reads better than upper-case, despite the latter being more legible, which would seem to indicate bouma is significant.
Even that exact question has been specifically investigated: the relative contribution of word shape and letter shapes. I believe it came out about 75% to 25% or something like that.John Savard said:
The question of how much significance is properly allocated to bouma is a complicated and difficult one, and I only have a very limited acquaintance with the facts involved; thus, I felt unprepared to wade into a debate with Hrant over that issue.