Regarding a site I built a few years back, I’ve been asked “Does the site support HTML5?”
The site was built a few years back using standard HTML.
What is the correct response to a question like this? I thought it was browsers which either support HTML5 or not as they render the script?
This is not really an appropriate question.
But your site will continue to work in browsers that support HTML4 and the doctype you are using. This support is likely to continue for quite some time.
You can easily start to move your site towards HTML5 by adding the HTML5 doctype:
<!DOCTYPE html>The HTML5 doctype is backwards compatible.
You can read some more here: How to write backwards compatible HTML5?