# Day (computer science)

One Day (pronounced [ Taeg ]; from English tag borrowed , for label , time , [waste] characters , labeller , trailer or tag ) is a markup Data with additional information.

## Markup languages

In some markup languages ( English markup languages ), such as SGML , XML , XHTML and HTML , called tags , the award marks or trademarks of elements in the documents.

In general, the following markings exist:

• <Elementname>- a starting day (in english start tag borrowed ) for the beginning
• </Elementname>- a closing tag ( English end tag ) for the end of an award
• <Leerelementname/>- a Leertag ( English empty element tag ), for example, in HTML for pictures, see the section " attributes "

The terms Elementnameand Leerelementnameare valid names for the respective markup language. A tagged document is written like this:

<Elementname>...</Elementname>
<Leerelementname/>


Interpreter applications, such as a web browser , read the markup marks from the document with a parser and thus receive the elements. They then use these for display purposes, for example. Elements and tags are directly related in fully marked documents: Pairs of start and end tags each represent exactly one element. An empty tag also forms exactly one element, one empty element.

### Attributes

Additional properties are assigned to an element with attributes. These are marked as follows after the element identifier within the start or empty day:

<Elementname Attributname="Attributwert">


An attribute consists of an assignment Attributname="Attributwert"(property name = property value ). The attribute value is usually in double (English "...") or in simple '...' quotes set - here the example of an embedded HTML image ( image ):

<img src="bild.jpg"/>


Sometimes there are also "Boolean attributes", for example in HTML, without a value assignment:

<video controls>


If the switch is controlsavailable, the attribute has the value "yes"; otherwise "no". In XML, however, this notation is prohibited.

Several attributes are listed separated by separators (spaces, tabs , line breaks):

<img src="bild.jpg" title="Abbildung"/>


### XML and XHTML

In XML and XHTML , tags must always be fully marked:

<p align="left">Text</p>


### SGML and HTML up to version 4

In SGML and HTML up to version 4, full markup is always permitted. However, depending on the DTD, minimizations are quite permissible. In the example, the attribute align="left"is leftminimized by:

<p left>Text</p>


### HTML version 5

In HTML version 5, the standard also allows full labeling. However, the standard labeling provides for minimizations.

A listing with full distinction:

<ul>
<li>erster Listeneintrag</li>
<li>zweiter Listeneintrag</li>
</ul>


is marked as follows in HTML version 5 (the end tags </li>are omitted):

<ul>
<li>erster Listeneintrag
<li>zweiter Listeneintrag
</ul>


## Simplified markup languages

In some simplified markup languages there are tags with square brackets or those that only consist of punctuation marks , and when using LaTeX as the markup language, "commands" with curly brackets are used - compare with the XML example above

\author{William Shakespeare}
\title{Ein Sommernachtstraum}


(this information is really difficult to avoid in a LaTeX source file ) - or for marking instead of the start and end tags of XML - cf. Markup language # Result and code in examples . In older word processing software, formatting instructions are given by "dot commands" ( troff and WordStar ) or similar. \begin{Tag}Element\end{Tag}

## File formats

When data is saved in files , a “tag” refers to meta or additional information that is appended to the file. In addition to the data to be saved, additional information, for example about its origin or purpose, is stored.

• The ID3 tag, for example, provides information about the title, genre, artist and other information in music files.
• A file format for image data that relies on the use of tags to store information is the Tagged Image File Format (TIFF).
• For additional labeling of any data, mostly photos, there is Exif .

## object oriented programing

In object-oriented programming , “tag” is used colloquially and has no precise definition. It denotes an attribute or data field which is either kept available for various purposes, but not necessarily used, or has a similar function as in XML and is used to classify program objects or to keep additional data available internally. In the latter case, often used synonymously with flag as a designation , the attribute remains hidden from a user or the programmer who uses ready-made classes .

In the Object Pascal variants Delphi and Kylix, for example, all classes have an integer field "Tag" which is not used at first and allows the programmer to temporarily store additional information there.

Under AmigaOS BOOPSI uses so-called tag lists for parameter transfer .

## Version management

In version control systems , a tag is used to mark a set of files from which a specific version can be restored at any point in time.

## Information architecture

In web design, tagging is a technique that allows every visitor to attach freely selectable terms to the pages they visit (the texts are, as it were, labeled). This allows articles to be sorted into different subject areas at the same time; the rigid hierarchy of the conventional navigation categories is thus supplemented or replaced.

## Networks

In the network area tags can be used to packages in a per VLAN divided power each VLAN segments associate and to packets for prioritization of traffic classes to mark ( Quality of Service ).

## Other uses

The technically imprecise use of the word can also cover other areas. All uses have in common that they are very closely based on the literal meaning of the English term. A “tag” is always an ( abstract ) label or tag, a label or some other type of marking.