The FPI is undoubtedly the least well-understood part of the document type declaration, an integral component of valid HTML, XML and Standard Generalized Markup Language (SGML) documents [REF].
A document type declaration (for HTML 4.01 strict[REF]) containing an FPI:<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> The FPI in the document type declaration above reads -//W3C//DTD HTML 4.01//EN[REF] .