lack of utility of XML Schemas for publishing. Some schema languages not only describe the structure of a particular XML format but also offer limited facilities to influence processing of individual XML files that conform to this format. DTDs and XSDs both have this ability; they can for instance provide the infoset augmentation facility and attribute defaults. RELAX NG and Schematron intentionally do not provide these. Related specifications A cluster of specifications closely related to XML have been developed, starting soon after the initial publication of XML 1.0. It is frequently the case that the term "XML" is used to refer to XML together with one or more of these other technologies that have come to be seen as part of the XML core. XML namespaces enable the same document to contain XML elements and attributes taken from different vocabularies, without any naming collisions occurring. Although XML Namespaces are not part of the XML specification itself, virtually all XML software also supports XML Namespaces. XML Base defines the xml:base attribute, which may be used to set the base for resolution of relative URI references within the scope of a single XML element. XML Information Set or XML Infoset is an abstract data model for XML documents in terms of information items. The infoset is commonly used in the specifications of XML languages, for convenience in describing constraints on the XML constructs those languages allow. XSL (Extensible Stylesheet Language) is a family of languages used to transform and render XML documents, split into three parts: XSLT (XSL Transformations), an XML language for transforming XML documents into other XML documents or other formats such as HTML, plain text, or XSL-FO. XSLT is very tightly coupled with XPath, which it uses to address components of the input XML document, mainly elements and attributes. XSL-FO (XSL Formatting Objects), an XML language for rendering XML documents, often used to generate PDFs. XPath (XML Path Language), a non-XML language for addressing the components (elements, attributes, and so on) of an XML document. XPath is widely used in other core-XML specifications and in programming libraries for accessing XML-encoded data. XQuery (XML Query) is an XML query language strongly rooted in XPath and XML Schema. It provides methods to access, manipulate and return XML, and is mainly conceived as a query language for XML databases. XML Signature defines syntax and processing rules for creating digital signatures on XML