Fast to type doesn't always mean short. It usually means that you should [AvoidSpecialCharacters] that are not available on the keyboards easily, and make it [ReadableMarkup], so that the user doesn't have to slow down to check if what he has written is what he means.

The need for excessive escaping of text can slow down typing considerably, so it's good if the markup is [CollisionFree].

Fast to type also means keeping the markup "linear" rather than "two-dimensional". For example, using parenthesised syntax to delimit block of text:

some block
of sample

you make it faster to type than by using indentation or markers on every line:

: some block
: of sample
: text

This becomes especially important when the text is not typed, but rather pasted and then the markup is added.