Program to check an HTML file. Errors detected: - Reference to undefined anchor name. - Duplicated anchor name. - Warning for unreferenced anchor name. - Unknown tag. - Badly formed tag. - Improper tag nesting. - Unescaped <, >, ", or &. - Bad escape string. - Improper embedding of attributes. - Bad (non-ascii) characters Advises on: - Use of <HTML>, <HEAD, <BODY> tags.