HTML/HTML entities

Some characters have special meaning in HTML, such as < and > for tags and & for entities, so you can't type them directly into content without confusing the parser. HTML entities solve this: &lt; renders <, &gt; renders >, &amp; renders &, and &quot; renders a double quote. They can be written as named entities (&copy;), decimal numeric references (&#169;) or hexadecimal ones (&#xA9;), and are also used for symbols that are hard to type like the euro sign or arrows.

A particularly important entity is &nbsp;, a non-breaking space that prevents a line break at that position and isn't collapsed like regular whitespace, though using it repeatedly for spacing is bad practice and CSS should be used instead. Entities also tie into security: escaping user-supplied text before inserting it into a page is a core defense against cross-site scripting, since it makes the browser treat dangerous input as text rather than markup.