Extensible markup language has certain specific rules governing which names can be used for its mark up object. A name consists of at least one letter that is from a to z or A to Z. If the name is of more than one character then it may start with an underscore or a colon. The initial letter of underscore can be followed by one or more letters, digits, hyphens, underscores, full stops and combining characters and ignorable characters. Spaces and tabs are not allowed in element names and the only punctuation signs allowed are hyphens and full stop. Extensible markup language is case sensitive, uppercase letters that is A to Z and lower case letters are recognized differently.
Also it stores the Extensible markup language documents with .xml extension. We know that hypertext markup language uses its tags as if they were style switches. The start tag turns a feature an, such as underlining, and an end tag turns it off again. Standard generalized markup language uses its start tags and end tags as containers. Together the start tag, the content and the end tag all form a single element. Element are the building bricks out of which an Extensible markup language document is assembled. Each Extensible markup language document must have only one root element and all the other elements are perfectly nested inside that element. Containers are those tags which hold or contain the text and other xml elements between the two tags.
As with hypertext markup language we can identify data using tags, thus collectively the tags are known as markup. But unlike hypertext markup language, Extensible markup language tags tell us what the data means rather than how to display it. Where an hypertext markup language tags says for example “display this text in bold” Extensible markup language offers a grammar or a syntax which can be used to create one’s own tag sets. These tags act like a field name in the program. It puts a label on a piece of data that identified it.
One can create any tags by sticking to the grammar; all Extensible markup language compliant applications are able to handle the tags in a uniform way. Extensible markup language was developed as document designers and content specialist realized that SGML and hypertext mark up language are simply too limited in scope to handle the many tasks, as not all content can be described as paragraphs, lists, tables and forms. Also Extensible markup language’s powerful linking mechanism allows us to link to material without requiring the link target to physically present in the object that is Extensible markup language opens possibilities for linking together things.