Hi,
I'm just getting going with a renderer that'll use MapCSS, and wanted to ask
some questions about the very basics of the semantics. The most important
thing that I can't get fixed in my head at the moment is whether a MapCSS file
specifies a bunch of statements that must be executed (causing the side effect
of some map being rendered) in order, or whether it specifies a bunch of
consistent rules that together can be queried to find the style of a particular
{node | way | relation}.
The first case doesn't seem to make too much sense. The limited documentation
covers merging styles, and rendering as you meet a statement seems to preclude
this (if it's on screen you can't merge the styles and render it again).
The second case doesn't seem to make much sense either though. No method of
evaluating the style of an object is specified. Suppose one rule specifies to
set tag a to x, while another specifies to set tag a to y. Which takes
precidence? Suppose 3 other rules depend on (respectively) a not being set, a
being x, and a being y, which of these rules apply? When should styles be
merged, and when should they be applied one on top of each other?
If someone could cover these basics I'd appreciate it.
Thanks
Tom Davie
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