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 majority of the pages are valid, but not all.
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
Some font size (less than 5%) are fixed and cannot be increased, or a less ideal feature using Javascript is being used.
"Description" is used to summarise the content of a HTML-page as short and incisive as possible. The content of this meta information is not shown to the user in the internet browser, but search engines do use them to a certain extent to evaluate the relevance of a site for the results page.
The description summarises the content in one sentence. The summaries are normally shown on the results page of search engines and contribute a great deal to the choice of web users.
Further information:
http://de.selfhtml.org/html/kopfdaten/meta.htm#beschreibung
Descriptions are either incomplete or not optimised on the tested website. Verify that the homepage and the sub-pages contain an appropriate description (a short and incisive sentence).
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A potential hint has been identified.
"Even though machine-level addressing like the URL should never have been exposed in the user interface, it is there and we have found that users actually try to decode the URLs of pages to infer the structure of web sites. Users do this because of the horrifying lack of support for navigation and sense of location in current web browsers. Thus, a URL should contain human-readable directory and file names that reflect the nature of the information space."
Source:
http://www.useit.com/alertbox/9605a.html
Further information:
http://www.w3.org/QA/Tips/uri-choose
The URL structure of the tested Website is generally good, though some complex URLs are used internally.
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A potential hint 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 alternative text for images, though the length of the alternative text is for one image at least outside the range between 8 and 80 characters. Alternative text which has correctly been recorded as empty will not return a negative result.
Using the ideal number of keywords can contribute to the searchability of a website. However, search engines may class it as "keyword spam" if too many keywords are used.
The number of keywords contained in the tested website is not optimal.
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A potential hint has been identified.