Walter Davis wrote in post #956434:
Rails 3 (last time I fooled with it, which was pre-release) shipped
with a completely HTML5 scaffold system, encouraging you to write your
own bits in HTML5 as well.
Yes, Item #6 below confirms my earlier thoughts about the optional
Start tags must have the following format:
1. The first character of a start tag must be a U+003C LESS-THAN SIGN
2. The next few characters of a start tag must be the element's tag
3. If there are to be any attributes in the next step, there must first
be one or more space characters.
4. Then, the start tag may have a number of attributes, the syntax for
which is described below. Attributes may be separated from each other by
one or more space characters.
5. After the attributes, or after the tag name if there are no
attributes, there may be one or more space characters. (Some attributes
are required to be followed by a space. See the attributes section
6. Then, if the element is one of the void elements, or if the element
is a foreign element, then there may be a single U+002F SOLIDUS
character (/). This character has no effect on void elements, but on
foreign elements it marks the start tag as self-closing.
7. Finally, start tags must be closed by a U+003E GREATER-THAN SIGN