Updates: Media (lyrics) has a new layout. I could never figure out how to lay it out, but it's easier to navigate now. I'm still working on a better duplicate Mamblog mod. I'm trying to make submittions easier but the poetry form died for some reason. Quizzes are also on their way from the old site. Joomla content isn't very code friendly so I'm having to rewrite old code. You can still click on News > AH v21 > Screen if you wish to use the quizzes.
At times, this specification recommends good practice for authors and user agents. These recommendations are not normative and conformance with this specification does not depend on their realization. These recommendations contain the expression "We recommend ...", "This specification recommends ...", or some similar wording.
The validity of a style sheet depends on the level of CSS used for the style sheet. All valid CSS1 style sheets are valid CSS2 style sheets. However, some changes from CSS1 mean that a few CSS1 style sheets will have slightly different semantics in CSS2.
A valid CSS2 style sheet must be written according to the grammar of CSS2. Furthermore, it must contain only at-rules, property names, and property values defined in this specification. An illegal (invalid) at-rule, property name, or property value is one that is not valid.
The document to which one or more style sheets refer. This is encoded in some language that represents the document as a tree of elements. Each element consists of a name that identifies the type of element, optionally a number of attributes, and a (possibly empty) content.
(An SGML term, see [ISO8879].) The primary syntactic constructs of the document language. Most CSS style sheet rules use the names of these elements (such as "P", "TABLE", and "OL" for HTML) to specify rendering information for them.
An element for which the CSS formatter knows only the intrinsic dimensions. In HTML, IMG, INPUT, TEXTAREA, SELECT, and OBJECT elements can be examples of replaced elements. For example, the content of the IMG element is often replaced by the image that the "src" attribute designates. CSS does not define how the intrinsic dimensions are found.
The width and height as defined by the element itself, not imposed by the surroundings. In CSS2 it is assumed that all replaced elements -- and only replaced elements -- come with intrinsic dimensions.
The content associated with an element in the source document; not all elements have content in which case they are called empty. The content of an element may include text, and it may include a number of sub-elements, in which case the element is called the parent of those sub-elements.
The content of an element after the rendering that applies to it according to the relevant style sheets has been applied. The rendered content of a replaced element comes from outside the source document. Rendered content may also be alternate text for an element (e.g., the value of the HTML "alt" attribute), and may include items inserted implicitly or explicitly by the style sheet, such as bullets, numbering, etc.
The tree of elements encoded in the source document. Each element in this tree has exactly one parent, with the exception of the root element, which has none.
An element A is called a descendant of an element B, if either (1) A is a child of B, or (2) A is the child of some element C that is a descendant of B.
An element A is called a sibling of an element B, if and only if B and A share the same parent element. Element A is a preceding sibling if it comes before B in the document tree. Element B is a following sibling if it comes after B in the document tree.
A user is a person who interacts with a user agent to view, hear, or otherwise use a document and its associated style sheet. The user may provide a personal style sheet that encodes personal preferences.
A user agent is any program that interprets a document written in the document language and applies associated style sheets according to the terms of this specification. A user agent may display a document, read it aloud, cause it to be printed, convert it to another format, etc.
Here is an example of a source document encoded in HTML:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN">
<HTML>
<TITLE>My home page</TITLE>
<BODY>
<h2>My home page</h2>
<P>Welcome to my home page! Let me tell you about my favorite
composers:
<UL>
<LI> Elvis Costello
<LI> Johannes Brahms
<LI> Georges Brassens
</UL>
</BODY>
</HTML>
According to the definition of HTML, HEAD elements will be inferred during parsing and become part of the document tree even if the HEAD tags are not in the document source. Similarly, the parser knows where the P and LIs end, even though there are no </P> and </LI> tags in the source.
This section defines conformance with the CSS2 specification only. There may be other levels of CSS in the future that may require a user agent to implement a different set of features in order to conform.
In general, the following points must be observed by a user agent claiming conformance to this specification:
It must support one or more of the CSS2 media types.
For each source document, it must attempt to retrieve all associated style sheets that are appropriate for the supported media types. If it cannot retrieve all associated style sheets (for instance, because of network errors), it must display the document using those it can retrieve.
It must parse the style sheets according to this specification. In particular, it must recognize all at-rules, blocks, declarations, and selectors (see the grammar of CSS2). If a user agent encounters a property that applies for a supported media type, the user agent must parse the value according to the property definition. This means that the user agent must accept all valid values and must ignore declarations with invalid values. User agents must ignore rules that apply to unsupported media types.
For each element in a document tree, it must assign a value for every applicable property according to the property's definition and the rules of cascading and inheritance.
If the source document comes with alternate style sheets (such as with the "alternate" keyword in HTML 4.0 [HTML40]), the UA must allow the user to select one from among these style sheets and apply the selected one.
Not every user agent must observe every point, however:
A user agent that inputs style sheets must respect points 1 - 3.
A user agent that renders a document with associated style sheets must respect points 1 - 5 and render the document according to the media-specific requirements set forth in this specification. Values may be approximated when required by the user agent.
The inability of a user agent to implement part of this specification due to the limitations of a particular device (e.g., a user agent cannot render colors on a monochrome monitor or page) does not imply non-conformance.
This specification recommends that a user agent allow the user to specify user style sheets.
In general, this document does not specify error handling behavior for user agents (e.g., how they behave when they cannot find a resource designated by a URI).
CSS style sheets that exist in separate files are sent over the Internet as a sequence of bytes accompanied by encoding information (see [HTML40], chapter 5). The structure of the transmission, termed a message entity, is defined by RFC 2045 and RFC 2068 (see [RFC2045] and [RFC2068]). A message entity with a content type of "text/css" represents an independent CSS document. The "text/css" content type has been registered by RFC 2138 ([RFC2318]).
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