You should also use a chart for "special and extended characters"...there may a clickable chart in your text-editor. Otherwise any decent HTML book will have one, although there are always a few characters left out.
That "xmp" tag is interesting...I haven't seen it before, but then I haven't bought an HTML book in the last year. Keep in mind, if this is a new or non-standards tag, some browsers may not understand it. This is why I recommend learning the special characters you use most often.
For example an ampersand ("&") followed by "lt" (less than) followed by a semicolon will give you the opening bracket, and using "gt" (greater than) instead of "lt" will give you the closing bracket. An ampersand followed by the word "copy" followed by a semicolon will give you the copyright symbol. Etc, etc.
Then you can use the "pre" tag surrounding your entire block of code...to make the font plain and monospaced. "Pre" has nothing to do with ignoring HTML code.