# Re: Percentages in CommonAbsolutePosition?

```Hello Vincent,

> So you wanna join the game? ;-)```
```
Well, sometimes it's hard to resist :-)

>> Normally you would assume that if you define a position wrt a
>> certain area (i.c. the page viewport), percentages are also
>> interpreted wrt to width and height of that same area.

> The added remark to the "left" property (7.6.5) states that it
> should be "interpreted in the prevailing coordinate system
> (established by the nearest ancestor reference area)".

You're right, and that would rule out the page viewport. Still I'd
like to think (and hope) that they simply forgot to add "...or, if
absolute-position has the value 'fixed', the page-viewport area" here.

The sections quoted below, when taken together, state that for fixed
areas, "left", "top" etc. should be interpreted immediately as
relative to the page-viewport:

4.2.2 Common Traits
(...)
Each area has the traits top-position, bottom-position left-position,
and right-position which represent the distance from the edges of its
content-rectangle to the like-named edges of the nearest ancestor
reference-area (or the page-viewport-area in the case of areas
generated by descendants of formatting objects whose absolute-
position is fixed);

4.9.1 Geometry
(...)
All areas in the tree with an area-class of xsl-fixed are positioned
such that the left-, right-, top-, and bottom-edges of its content-
rectangle are offset inward from the content-rectangle of its
ancestor page-viewport-area by distances specified by the left-
position, right-position, top-position, and bottom-position traits,
respectively.

5.5.4 Absolute-position Property
If absolute-position has the value "absolute" or "fixed", the values
of the left-position, top-position, etc. traits are copied directly
from the values of the "left", "top", etc. properties. Otherwise
these traits' values are left undefined during refinement and
determined during composition.

So, at the moment, it seems that we can all take our pick depending on
what we prefer. Time for official clarification indeed. Personally I
hope that: a) percentages and explicit lengths should always be
interpreted in the same coordinate system, and b) for absolute and
fixed areas, that this coordinate system is always the ancestor which
the area is "attached to" (nearest ancestor-ref and page-vp,
respectively).

Kind regards,
Paul Vinkenoog
```