Datasheet

❑ Opening and closing elements: All XML elements must have a closing element. Omitting a

closing element will cause an error. Exceptions to this rule is the XML definitional element at the

beginning of the document, declaring the version of XML in exceptions, and an optional style

sheet:

<root>

<branch_1>

<leaf_1>

</leaf_1>

</branch_1>

<branch_2>

</branch_2>

</root>

HTML tags do not always require a closing tag. Examine the first HTML code example in this chapter

in the section “Comparing HTML and XML.” The first paragraph does not have a

paragraph end

tag. The second paragraph does have a

paragraph eng tag. Some closing tags in HTML are

optional, meaning that a closing tag can be included or not.

❑ Case sensitive: XML elements are case sensitive. HTML tags are not case sensitive. The XML

element <root> in the previous example is completely different than the XML element <Root>

in the next example. The following example is completely different than the previous XML doc-

ument shown in the previous point. Even though all the elements are the same, their case is

different for the

<Root> and <BRANCH_1> elements:

<Root>

<BRANCH_1>

<leaf_1>

</leaf_1>

</BRANCH_1>

<branch_2>

</branch_2>

</Root>

HTML does not require proper nesting of elements, such as in this example:

This is bold italic text in red

XML on the other hand, produces an error using the preceding code. For example, in XML the

following code is invalid because

</tag2> should appear before </tag1>:

❑ Element attributes: Like HTML tags, XML elements can have attributes. An element attribute

refines the aspects of an element. Attributes and their values are called name-value pairs.

An XML element can have one or more name-value pairs, and the value must always be

quoted. HTML attribute values do not always have to be quoted, although it is advisable. In the

following XML document sample (the complete document is not shown here), populations for

continents (including the name of the continent) are contained as attributes of the

element. In other words, the continent of Africa had a population of 748,927,000 people in 1998

(748 million people where the population in thousands is the total divided by 1,000, or 748,927).

Chapter 1

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