Use of valid HTML source code

HTML is a platform-independent document description language in which web pages are written.

" HTML is not a programming language. Because with HTML you cannot control a robot, create variables or program a game, for example". (Source)

The website you are currently on is also HTML. It contains the structure and content of this page. The design and layout are stored in separate stylesheet files (CSS).
These documents or pages are usually viewed in a web browser such as Mozilla Firefox, Opera, Internet Explorer or Safari.

In addition, the documents are also read by the search robots of search engines such as Google, Yahoo, Microsoft Network or AltaVista.

Special attention is also paid to disabled users, some of whom use special software, which the website outputs acoustically via a Braille display, for example.

In all cases, the software depends on the best possible HTML source code.

Documents that are not valid or violate standards rely on the error correction of the software that reads them (browser, robot, screen reader etc., see above). However, this error correction varies greatly depending on the software used, which can lead to errors, and in many cases without the website operator noticing, because it is impossible to fully test the website again via all this software after each update.

Non-valid HTML source code often causes high costs, especially because of unnecessary troubleshooting and non-optimal operation or even annoyance of the users.

Further information:
The validity of HTML source code can be checked via so-called validators.

Link recommendations:

Abbreviations:
HTML: HyperText Markup Language