You have not submitted these variable(s) by a form:

bookid: The name of the main XML file without the extension. It's also the folder name where the xml documents are stored.

pathtoImg: URI to the folder where the images of pages arestored. Ex: '../images/114/' Note: It has to end with a '/'.

pathtoXML: URI to the folder where the XML documents arestored. Ex: '../xml/tuber101/' Note: It has to end with a '/'.