perm url with updates: http://xahlee.org/js/css_problems.html
Xah Lee, 2010-01-28
Some random thoughts about CSS.
Am reading the Wikipedia article on Cascading Style Sheets again.
Here's a interesting quote:
While new additions to CSS3 provide a stronger, more robust layout feature-set, CSS is still very much rooted as a styling language, not a layout language. This problem has also meant that creating fluid layouts is still very much done by hand-coding CSS, and make the development of a standards-based WYSIWYG editor more difficult than expected.
This is so very much true. For example, if you want text to flow in 2 columns, basically you have to manually move the the text to the appropriate block. (as opposed to, for example, text being auto word wrapped by a specified width when the text is long. See: CSS Text Wrapping)
Also, although you can make a page's layout using CSS instead of Tables, but if you want more fine grained layout, such as using nested tables, CSS pretty much fails. You'd spend several hours trying do it and come out with unsatisfactory result. (see also: Tableless Layout with CSS) I'd say, just use tables.
CSS's tag matching scheme (so-called Selectors) is also pretty weak and ad hoc. For example, there's “:first-child” to match the first child of a tag, but you can't match second child, third, etc, or last. “AAA + BBB” will match BBB only if there exist in the same level a AAA, and comes before it. But, you can not specify a match where there must be a CCC that comes after.
Generally speaking, html and xml are tree structures. With this perspective, you can see that css selectors are just a way to match tree branches. With a tree, you have concepts of root, level/depth, parent/child/siblings, ordering of siblings. For a tree matcher, in its full generality, you can consider a scheme where all these tree properties can be specified. (in a way, similar to pattern matching in functional languages.) Of course, css isn't a computing language, so, for designing its Selector, efficiency needs to be considered. In any case, the way css's seletors is today, is rather ad hoc and very weak.
Also, the selector expression can not use parens to specify precedence. This is a need i actually had a few times for my own site. (it'll take some time to write explanation. Will have to add example here later.)
Two other criticisms from Wikipedia i particularly find to be important are:
CSS offers no way to select a parent or ancestor of an element that satisfies certain criteria. A more advanced selector scheme (such as XPath) would enable more sophisticated style sheets. However, the major reasons for the CSS Working Group rejecting proposals for parent selectors are related to browser performance and incremental rendering issues.
While horizontal placement of elements is generally easy to control, vertical placement is frequently unintuitive, convoluted, or impossible. Simple tasks, such as centering an element vertically or getting a footer to be placed no higher than bottom of viewport, either require complicated and unintuitive style rules, or simple but widely unsupported rules.[clarification needed]
For a short tutorial of css selectors, see: What's New in CSS2.