Some HTML element types have no content. Element names are always case-insensitive. Elements are not tags. For instance, the HEAD element is always present, even though both start and end HEAD tags may be missing in the markup. They may appear in any order.
Tags are case-insensitive .
You can write them in small letters, big letters, or any mixture. A common convention is to write them in caps so they stand out from the rest of the document. White space and line breaks will not affect the document appearance in a browser except when used inside certain special tags which we'll describe later. Some people find HTML can be hard to read. This need not be so if it's written tidily.