– Depending on the type of markup you’re using, there may be certain tricks that aren’t allowed.
– It influenced how a browser interprets your web page. If you don’t include a doctype on your web page, Internet Explorer switches itself into a quirks mode. While IE is in this mode, certain information details are details are processed in inconsistent, nonstandard ways. For example If you have a web page that looks dramatically different in Internet Explorer than it does in Firefox, the basic reason may be a missing or invalid doctype.If you’re working with an existing website that’s based on the somewhat out-of-date HTML standard, this is the doctype you need:
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.01//EN”“https://www.w3.org/TR/html4/strict.dtd”>