Horizontal positioning and leaders

[bertfrees]

Describe in more detail the behavior of the leader() function. Currently text that follows a leader is being right aligned at the right edge of the block. This is the most important use case of leaders, but it only allows for two "columns". Find out if there are other use cases and if maybe we need some kind of "tab stops" feature as known in word processors.

See http://braillespecs.github.io/braille-css/#leaders

[bertfrees]

The definition of the leader function could become

leader( <braille-string> [ , <position> [ , <alignment> ] ] )

where

• <position> is an absolute length (distance from left content edge or left edge of page area) or a percentage (distance from left content edge expressed in a percentage of the total width of the containing block)
• <alignment> is "left", "centered" or "right"

The defaults are "100%" and "right".

This definition maps 1 on 1 to http://braillespecs.github.io/obfl/obfl-specification.html#L1207.

[bertfrees]

The position should be allowed to exceed 100%, which makes it possible to create a text indent on the last line on the right side.