HTML is a mark-up language used to create websites, and is independent of platforms.
"HTML is not a programming language, since HTML does not allow to, say, control a robot, set a variable or programme a game." (Quelle)
The display of invalid or incorrect documents depends on the software reading them (browser, roboter, screenreader, etc; see above). However, the display will vary greatly depending on the software, and this can lead to errors, often without the knowledge of the website manager, since it is impossible to test the website against all updates of all the software.
Non validated HTML source text can cause high costs, especially if it causes the software to look for an error or if the functionality and therefore the user experience is impacted.
Further information:
The validity of the HTML source text can be checked with a so-called 'validator'.
Examples:
Further information
http://blog.antikoerperchen.de/beitrag/28/validierung-wozu-warum-valider-html-code-wichtig-ist.html
Acronyms:
HTML: HyperText Markup Language
The tested website appears to use XHTML, but the source text contains errors. Use the Qualidator SiteAnalyzer to find the errors on your site. Please note that it is not sufficient to validate the homepage only. To optimise access it is necessary that all pages are validated, so that display errors in various browsers can be avoided.
Pop-ups tend to annoy web users, as they appear suddenly and cannot be controlled. In addition, many users associate pop-ups with untrustworthy gambling and porn sites. User-friendly websites should therefore not include pop-ups, with the following exception: a print-preview of a page displayed as a pop-up.
Source:
"Prioritizing Web Usability" by Jakob Nielsen/Hoa Loranger
Further information:
http://www.usability.ch/Alt_nav/Alertbox/NJ_20041206.htm
The tested website is coded to display pop-ups.
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A potential warning has been identified.
Separating design and structure of the website carries great advantages. The sharper the distinction, the more independent the two areas are. A lack of such a distinction is also called a "spaghetti mark-up" or a "tag-soup" (from the term "HTML tag").
Nowadays it is easy to save colours, type fonts, design images and to a large extent even the layout of the website in CSS files (CSS = Cascading Style Sheet).
Further information:
http://www.style-sheets.de/guide/grundlagen/warum_css
http://www.vorsprungdurchwebstandards.de/theory/retro-coding/
Hint for IT technicians: "Code" does not refer to javascript, but to HTML source.
The tested website contains spaghetti mark-up; morevover, it is not or not fully defined in CSS Format.
The logical connection between definition and form field is missing if the form fields lack an explicit title.
This means that in the instance of a linear form, it is not apparent which definition belongs to which fiels. This is why the element LABEL was introduced with the attribute for, allowing the explicit definition for form fields.
Using the element LABEL allows Screen-Readerusers in particular to view the definition of the form field directly in the form field itself.
Source:
http://www.barrierefreies-webdesign.de/knowhow/formulare/label.html. Further information can be found in the W3C accessibility guidelines (12.4 Associate labels explicitly with their controls, Guideline 12, Accessibility Guidelines for Web Content 1.0, W3C recommendations 5th May 1999http://www.w3c.de/Trans/WAI/webinhalt.html) und http://de.selfhtml.org/html/formulare/strukturieren.htm.
Form fields on the tested website do not contain correct labels.
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A potential warning has been identified.
Alternative text is displayed if an image cannot be downloaded or if the mouse pointer is moved over the image*. The alternative text is on one hand important for visually impaired visitors, using an audio tool to read the content of the website and the alternative text of images.
On the other hand, alternative text can also be recognised by search engines. Alternative text needs to be phrased in a meaningful manner, though it should not be a detailed description of the image.
Further information:
http://www.bjoernsworld.de/html/alt-text.html
http://webdesign.crissov.de/alt-Text#Start
* Internet Explorer shows alternative text as a tooltip if the mouse pointer is rested on the image. This is not prohibited but it can annoy page authors. It does also indicate that the alt-attribute refers to this tooltip, which is wrong. Should you want to add a descriptive tooltip to your images, make use of the attribute "title".
Quelle: http://de.selfhtml.org/html/grafiken/einbinden.htm#referenz
The tested website contains undefined alternative text. This needs to be specified as "empty", especially for images which are not part of the visible content.
Older web projects were often designed with so-called "empty images" (i.e. images without content, used as placeholder). This technique is now outdated and should be replaced with CSS features such as "Padding" and "Margin". This allows an increased performance of the website, as well as a strict separation between design and content, and an abstraction of the design from the structure.
Further information:
http://seybold.jan-andresen.de/05killer.php
The tested website contains blank images.