XML has a small but flexible set of plain-text notations. Labels or markup , which identify the different parts or elements of a document , are embedded as character-strings within the text to indicate the start and end of a section. The document designer defines the element names. Elements can be nested.
Data occurs as element content or as attributes .
The document is the unit of encapsulation, often corresponding to a disk-file. The syntax allows complex data which has a tree structure to be encapsulated in text streams or documents for transfer. Additional syntax allows full normalisation and recording of more complex datamodels, such as graphs, by making links between different parts of documents or between documents. Many specific XML based formats have been designed. Of immediate interest amongst the general purpose formats are those in the graphics area.