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.
The content of the website needs to be well structured with logical and meaningful titles (h1, h2, h3...). Meaningful words which are important for the understanding of the text, need to be placed at the beginning of the title, as web users mainly only perceive the first few words of a title. Titles should be no longer than 60 characters.
Titles can also have a positive impact on search machine rankings.
Source and further information:
"Prioritizing Web Usability" by Jakob Nielsen/Hoa Loranger.
The tested website does not comply with this requirement.
Marking previously visited hyperlinks helps users to identify which pages of the website have previously been read. In other words, according to Nielsen the navigation interface should answer three essential questions: "Where am I?", "Where have I been?" and "Where can I go?"
Source and further information:
"Prioritizing Web Usability" by Jakob Nielsen/Hoa Loranger and "Designing Web Usability" by Jakob Nielsen
The tested website does not support fully this type of marking.
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A potential warning has been identified.
Not all visually impaired people make use of technical support to navigate on the internet. The feature to increase fonts is an important element to ensure that all information of the website can be read by all users. Even people who are not visually impaired need to increase the font sometimes. At the same time, an increasing number of older people surf the web; they too need a feature to increase the font. To this purpose, it is important to define the font size not in pixel, but in percentage or "em".
Source and further information:
"Prioritizing Web Usability" by Jakob Nielsen/Hoa Loranger
The font on the tested website cannot be increased and defined with the automated browser feature "Text Size".
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.
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.