1. A method comprising: receiving a request for a markup language source document; identifying a manifest document associated with the requested markup language source document; determining to select, from a plurality of overlay documents, at least one overlay document that fulfills an attribute condition specified in the manifest document, wherein the markup language source document specifies one or more overlay document versions with which the markup language source file is compatible, wherein when the markup language source document comprises a section of markup language that specifies that the section is designated as immutable to prevent modification via the at least one overlay document, a directive of immutability is selected from a group comprising: prevention, of a specified attribute of the section, from modification by the at least one overlay document; prevention, of specified content of the section, from modification by the at least one overlay document; and prevention, of a specified structure of the section, from modification by the at least one overlay document; in an event no overlay document is selected, in response to the request, returning the markup language source document; and in an event at least one overlay document is selected: providing an interface for the at least one overlay document to modify the presentation of the markup language source document, wherein when an associated version of the at least one overlay document is not compatible with the markup language source document, the interface utilizes an associated document to upgrade the at least one overlay document to another version, wherein no special tags or other types of markers are required in the markup language source document to enable modification of the presentation of the markup language source document as specified by the at least one overlay document, the interface having a plurality of functions for modifying the presentation of the markup language source document, the functions comprising: modifying element content; modifying element attributes; removing elements; adding elements; rearranging elements; and stylization of elements; generating a modified markup language source document by applying the at least one overlay document to the requested markup language source document; and in response to the request, returning the modified markup language source document.
1. A method comprising: receiving a request for a markup language source document; identifying a manifest document associated with the requested markup language source document; determining to select, from a plurality of overlay documents, at least one overlay document that fulfills an attribute condition specified in the manifest document, wherein the markup language source document specifies one or more overlay document versions with which the markup language source file is compatible, wherein when the markup language source document comprises a section of markup language that specifies that the section is designated as immutable to prevent modification via the at least one overlay document, a directive of immutability is selected from a group comprising: prevention, of a specified attribute of the section, from modification by the at least one overlay document; prevention, of specified content of the section, from modification by the at least one overlay document; and prevention, of a specified structure of the section, from modification by the at least one overlay document; in an event no overlay document is selected, in response to the request, returning the markup language source document; and in an event at least one overlay document is selected: providing an interface for the at least one overlay document to modify the presentation of the markup language source document, wherein when an associated version of the at least one overlay document is not compatible with the markup language source document, the interface utilizes an associated document to upgrade the at least one overlay document to another version, wherein no special tags or other types of markers are required in the markup language source document to enable modification of the presentation of the markup language source document as specified by the at least one overlay document, the interface having a plurality of functions for modifying the presentation of the markup language source document, the functions comprising: modifying element content; modifying element attributes; removing elements; adding elements; rearranging elements; and stylization of elements; generating a modified markup language source document by applying the at least one overlay document to the requested markup language source document; and in response to the request, returning the modified markup language source document. 3. The method as recited in claim 1 , wherein identifying a manifest document comprises: determining that a filename associated with the markup language source document matches a filename specified in the manifest document.