The HTML is used to mark up text whereas XML is used to mark up data.
The HTML is used for UI displaying purpose but the XML is used for data representation.
The HTML uses a fixed, unchangeable set of tags but in XML, you make up your own tags.
What Is a valid XML document?
If a document is structurally correct (with the above well-formed XML rules) then it can called as valid XML documents.
How does the XML structure is defined?
The Extensible Markup Language (XML) document will have a structure which has to be defined before we can create the documents and work with them. The structural rules can be defined using
many available technologies, but the following are popular way of doing so,
1) Document Type Definition (DTD)
What Is DTD?
The DTD stands for Document Type Definition and used to define the legal building blocks of an XML document.
DTD defines rules for a specific type of document i.e.
1. Names of elements
2. Order of elements
3. Proper nesting and containment of elements
4. Element attributes
What Is XML Schema Element?
The schema element defines the root element of a schema.
As an Example,
<xs:element name="values" type="xs:string" />