For the most part, characters within HTML documents that are not part of a tag are rendered as-is by the browser. However, some characters have special meaning and are not directly rendered, while other characters can't be typed into the source document from a conventional keyboard. Special characters need either a special name or a numeric character encoding for inclusion in an HTML document.
As has become obvious in the discussion and examples leading up to this section of the book, three special characters in HTML source documents have very special meaning: the less-than sign (<), the greater-than sign (>), and the ampersand (&). These characters delimit tags and special character references. They'll confuse a browser if left dangling alone or with improper tag syntax. So you've got to go out of your way to include their actual, literal characters in your HTML documents. The only exception to this is that these characters may appear literally within the <listing> and <xmp> tags.
Similarly, you've got to use a special encoding to include double quotation mark characters within a quoted string, or when you want to include a special character that doesn't appear on your keyboard but is part of the ISO Latin-1 character set implemented and supported by most browsers.
To include a special character in your HTML document, you enclose either its standard entity name or a pound sign (#) and its numeric position in the Latin-1 standard character set inside a leading ampersand and an ending semicolon, without any spaces in-between. Whew. That's a long explanation for what is really a simple thing to do, as the following example illustrates. The example23 shows how to include a greater-than sign in a snippet of code by using the character's entity name. It also demonstrates how to include a greater-than sign in your HTML text by referencing its Latin-1 numeric value:
 The popular ASCII character set is a subset of the more comprehensive Latin-1 character set. Composed by the well-respected International Organization for Standardization (ISO), the Latin-1 set is a list of all letters, numbers, punctuation marks, and so on, commonly used by Western language writers, organized by number and encoded with special names. Appendix E, Character Entities contains the complete Latin-1 character set and encoding.
if a > b, then t = 0 if a > b, then t = 0
Both examples cause the text to be rendered as:
if a > b, then t = 0
The complete set of character entity values and names are in Appendix E, Character Entities. You could write an entire HTML document using character encoding, but that would be silly.