Bug 60064

The present semantics for tab stops require extensive manual editing when changing the final document size or orientation to keep the layout in sync with the intended design (e.g. switching from DIN to US format or from portrait to landscape).

A simple example in TOC (table of contents)
A TOC entry has 3 components: section number, title and page number. To nicely align these components, a style with 2 tab stops is defined: the first one as, say, 2cm, left align; the second as 17cm (DIN A4 - two 2cm page margins), right align.
Now, document is switched to landscape. The style must be edited to change the second tab stop to 27.7cm. If the document is transmitted to the US, style must again be updated for US stationery.

This trouble could be avoided if tab stops were relative to some user-defined origin position instead of the default left margin (in left-to-right writing systems; transpose for RTL).

This origin should be user-positioned anywhere between the margins of the current paragraph as a percentage: 0% means left margin, 50% center, 100% right margin, etc. By default, tab stops are relative to origin 0% (compatible with the present design).

TOC example solved as:
first tab stop unchanged at 2cm, origin 0%, left
second tab stop at 0cm, origin 100%, right

I do not think values outside 0-100% should be allowed because you cannot rely on proportions between the current paragraph dimensions and the gutter, page, ... However, this does not preclude tab stops from having negative coordinate or big positive values to set text in the left/right margins or gutter.

With such an attribute, whenever an area (page, table, table cell, paragraph, ...) definition change occurs, absolute tab stop coordinate are recomputed and the intended layout is kept without user intervention.

This feature could even be refined to be document-designer-friendly: if the origin position is itself named (i.e. styled like bullet or numbering styles), experimenting with layout can be very easy. Again an example:
Presenting a list of words in tabular form with a leading term at the left and two associated terms to be set symmetrically from some position. This is solved as:
- tab stop at 1cm, 0%, left (or no tab stop)
- tab stop at -1cm, 75%, right
- tab stop at +1cm, 75%, left
If the 75% origin has a name/style, the 75 number can be adjusted in a single place to try for the value giving the best layout instead of adjusting individual tab stops.

Thank for comments
ajlittoz