On forms and tables
Disclaimer: This page only exists because my grey cells are full. Whenever something new comes up, my brain has to throw out old memories to free up some space. And information on HTML forms and tables seems to have drained off at some point. I simply cannot remember it all. Consequently, I return to this collection of bits and pieces whenever the need arises. So there.
In the back of my mind
The information below has been shamelessly copied from a plethora of sources. Well, a few, at least. And before its gone: The quotes may dissonant slightly with their sources. A readability thing, really.
On forms
Do not use the placeholder attribute instead of label; its purposes are different. label describes the role of the form (i.e. it indicates what kind of information is expected), and the placeholder is a hint about the format that the content should take. There are cases in which the placeholder is never displayed to the user, so the form must be understandable without it.
On tables
Up front: Many table elements are not required but will add useful information to people with screenreaders.
Applied to the table tag, the summary attribute was earlier used to describe the content of a table. Now, however, it is deprecated. Use e.g. the caption element instead.
A table’s caption basically acts as a heading for the table.
thead, tbody, and tfoot break a table into logical sections. For instance, all the column headings can be placed inside the thead element, providing a means of separately styling that particular area. If a thead or tfoot element is used, one (or more) tbody element(s) must be used. Only one thead and tfoot element can be used in a table, but there is no restriction on tbody elements. MDN adds: The tfoot must appear after any caption, colgroup, thead, tbody, or tr element. This is the requirement as of HTML5.
Row and column headings should be marked up as th rather than td, although if something is both a heading and data it should be left as a td. Table headings can be given a scope attribute of row or col to define whether they are row or column headings. They can also be given a value of rowgroup or colgroup if they relate to more than one row or column.
While the tr element makes it possible to style whole rows, it is more difficult to apply a style to an entire column. The colgroup and col elements may solve the problem, but they are not (are they?) supported by all browsers.
References
1. MDN on input
2. Andy Budd, CSS Mastery: Advanced web standards solutions (2006)
Remaining references are linked to in the text.