The main building blocks of both XML and HTML documents are Elements.

Examples of HTML elements are "body" and "table".
Examples of XML elements could be "note" and "message".
Elements can contain other elements(child elements), text, or be empty.
Examples of empty HTML elements are "img", "br" and "hr".

An element is made up of a start and end tag with data in between. The tags describe the data. The data is called the value of the element.

Attributes provide extra information about elements.

Always, attributes are placed inside the starting tag of an element. It always come in name/value pairs. The following "img" element has additional information about a source file:

The name of the element is "img". The name of the attribute is "src". The value of the attribute is "flower.jpg". Since the element itself is empty it is closed by a " /".

Entities are characters which have a special meaning.

The following entities are predefined in XML:

PCDATA means parsed character data.

Elements have values. If a value has tags representing child elements, these tags need to be expanded or parsed and handled as separate elements.

CDATA means character data.

The value of an element is treated as a single item and is not expanded. This is text that will not be parsed further by whatever application is processing your marked up document. If this text contains any entities they will not be replaced with their value, and any markup will not be treated as markup.