Single quote marks can be included within the attribute value when the value is delimited by double quote marks, and vice versa. In certain cases, it is possible in HTML to specify the value of an attribute without any quotation marks. We suggest using quotation marks even when it is possible to eliminate them. Attribute names are always case-insensitive.
Single quote marks can be included within the attribute value when the value is delimited by double quote marks, and vice versa.
In certain cases, it is possible in HTML to specify the value of an attribute without any quotation marks. We suggest using quotation marks even when it is possible to eliminate them. Attribute names are always case-insensitive. Attribute values are generally case-insensitive.
The definition of each attribute in the reference manual indicates whether its value is case-insensitive. HTML documents may compress better if you use lower case letters for element and attribute names.
The reason is that the compression algorithms do a better job for more frequently repeated patterns, and lower case letters are more frequent than upper case ones. Similary, user agents must not render SGML processing instructions e. Though cryptic and dissuasive at first, the DTD fragment gives concise information about an element and its attributes.
We have chosen to include the DTD fragments in the specification rather than seek a more approachable, but longer and less precise means of describing an element. While almost all of the definitions include enough English text to make them comprehensible, for those who require definitive information, we complete this specification with a brief tutorial on reading the HTML DTD.
Block level and Inline elements Certain HTML elements are said to be "block level" while others are "inline" also known as "text level". The distinction is founded on several notions: Content model Generally, block level elements may contain inline elements and other block level elements.
Generally, inline elements may generally contain only data and other inline elements.
Inherent in this structural distinction is the idea that block elements create "larger" structures than inline elements. Formatting By default, block level are formatted differently than inline elements. Block level elements generally begin on new lines, inline elements generally do not.
Block level elements end an unterminated paragraph element. This enables you to omit end-tags for paragraphs in many cases. Directionality For technical reasons involving the [UNICODE] bidirectional text algorithm, block level and inline elements differ in how they inherit directionality information.
For details, see the section on inheritance of text direction. Style sheets provide the means to specify the rendering of arbitrary elements, including whether an element is rendered as block or inline.
In some cases, such as an inline style for list elements, this may be appropriate, but generally speaking, authors are discouraged from overriding the conventional interpretation of HTML elements in this way.
The alteration of the traditional presentation idioms for block level and inline elements also has an impact on the bidirectional text algorithm.
See the section on the effect of style sheets on bidirectionality for more information. In the DTD, comments are delimited by a pair of "--" marks, e. When the macro is referred to by name in the DTD, it is expanded into a string.
These names are expanded recursively. They are used when the content model includes inline and block level elements respectively.
Between these are specified: Whether the element's end tag is optional. Two hyphens that appear after the element name mean that the start and end tags are mandatory. One hyphen followed by the letter "O" not zero indicates that the end tag can be omitted.
A pair of letter "O"s indicate that both the start and end tags can be omitted. The element's content, if any. The allowed content for an element is called its content model. Elements with no content are called empty elements. The two hyphens indicate that both the start tag and the end tag for this element are required.
The content model for this element defined to be "at least one LI element". We describe content models in detail below. This example illustrates the definition of an empty element:A markup language defined using SGML or XML has a specific vocabulary (labels for elements and attributes) and a declared syntax (grammar defining the hierarchy and other features).
Conceived notionally in the s - s, the Standard Generalized Markup Language (SGML, ISO ) gave birth to a profile/subset called the Extensible Markup Language (XML), published as a W3C .
About SGML. The Standard Generalized Markup Language (SGML, defined in), is a language for defining markup languages. HTML is one such "application" of SGML. An SGML application consists of several parts: The SGML declaration.
The SGML declaration specifies which characters and delimiters may appear in the application. SGML is an ISO standard: "ISO Information processing – Text and office systems – Standard Generalized Markup Language (SGML)", of which there are three versions: Original SGML, which was accepted in October , followed by a minor Technical Corrigendum.
The Standard Generalized Markup Language (SGML ; ISO ) is a standard for defining generalized markup languages for documents. ISO Annex A.1 defines generalized markup: Generalized markup is based on two postulates.
Markup should be declarative: it should describe a document's structure and other attributes, rather than specify the processing to be performed on it.
SGML, Standard Generalized Markup Language, is an enabling technology used in applications such as HTML. (see: Toward a Formalism for Communication on the Web). The HTML specifications assume a working knowledge of SGML. The SGML standard . SGML is used widely to manage large documents that are subject to frequent revisions and need to be printed in different formats.
Because it is a large and complex system, it is not yet widely used on personal computers.