The representant of the Google, John Mueller, told in a Google Conference that is recommended to own a website that has a valid HTML.
This rule came recently with the change of our policy. It is very important to use a valid HTML.
Is it a very important fact and we should care about this?
No, because websites with a broken HTML will not be removed from the index because the search results will be very few.
However, there are some important things that should be considered. A very rare thing, if the website has a very broken HTML, it will be very hard to index because it can’t be picked. Another important thing is that when HTML is broken, the structured data are very difficult to be picked up, so you will need a validator to save your structured data. Another very important thing is that if HTML is broken it will be more difficult for newer devices to process it.
The conclusion of this thing
You will not be punished if you use a broken HTML because the Google search engine has no problems with them.
Even if Google allows this, it is recommended to own a valid HTML for your website because if you have a valid HTML it means that the site is a good one. A quality website means more visitors and customers, and this is something that everybody wants. The success of a website lies in its quality; it is a very important thing that should be known by the owners of sites who want to succeed in the Internet world.
Factors that could disturb your website
There are many things that could disturb the place of your website on Google search engine. If you want to be sure that your website goes well you should try the website audit tool from SEOprofiler.