Syntax is, however, important and in some cases, for some browsers, crucial. There are cases when an attribute must be enclosed in quotes for instance. We'll learn about these as they arise. HTML defaults and attributes Many HTML tags can have attributes that modify the functions, options or features of the tag. The corollary is that tags that can have attributes have defaults.
Physical tags describe a document's layout .
Some tags are seen only by computer programs, and are invisible to the person viewing the page with their browser. These tags are read by the browser but not displayed on the page, and by search engines and their robots. This is where search engines get the titles of pages that it displays in its results. It also determines how bookmarks and favorites identify a page, and it is usually displayed in the top grey bar of the browser window. There are many of these, they are not necessary, but they give additional information to search engines like descriptions of the page, and lists of keywords.