Is XHTML Element Name Case Sensitive?

Yes, XHTML element names are case sensitive. All element names must be written in lower case letters.

What Is Wrong with My "checked" Attribute Values?

Attribute "checked" is an optional attribute for XHTML element "input". In XHTML specification, attribute "checked" has only predefined value: "checked". However, in HTML specification, attribute "checked" requires no value.

If you are converting existing HTML documents to XHTML format, you will get some syntax error on your pre-selected items in radio buttons, check boxes and dropdown lists, "checked" attributes are used without any values.

What is a "span" Tag/Element?

A "span" element is an inline element that you can use a container of inline elements and text contents. By default, browsers will do nothing on "span" elements unless specify some CSS properties in them. Here are basic rules about an "span" element:

1. "span" elements are inline elements.
2. "span" elements can have PCDATA as contents.
3. "span" elements can have inline elements as sub-elements.
4. "span" elements can not have any block elements as sub-elements.
5. A "span" element will be ignored by most browsers, unless it has some CSS properties.