A detailed introduction to the use of tags and elements in XML

This article mainly introduces the use of tags and elements in XML. It is the basic knowledge for introductory learning of XML. Friends who need it can refer to it

tag
us Let's learn about one of the most important parts of XML, XML tags. XML tags are the basis of XML. They define the scope of an element in XML. They can also be used to insert comments, declare settings required for the parsing environment, and insert specific directives.

XML tags can generally be classified as follows:

Start tag
Each starting non-empty XML element is marked as a start tag. Here is an example of a start tag:

<address>

End tag
Every element with a start tag should be closed with a closing tag. Here is an example of a closing tag:

</address>

Note that the closing tag contains a slash ("/") in front of the element name.

Empty tag
The text that appears between the start tag and the end tag is called content. Elements with no content are called empty elements. Empty elements are represented in the following two ways:

(1) The start tag is followed by an end tag, as shown below:

<hr></hr>

(2) In the true sense The empty element tag looks like this:

<hr />

The empty element tag can be used for any element that has no content.

XML tag rules
The following are the rules to follow when using XML tags:

Rule 1

XML tags are case-sensitive. The following line of code is an example of bad syntax because the two tags are not the same case, which is considered bad syntax in XML.

<address>This is wrong syntax

The following code shows the correct approach, where the opening and closing tag names use the same case.

<address>This is correct syntax</address>

Rule 2

XML tags must be closed in the appropriate order, for example, an XML tag opened inside another element must be closed before the outer element is closed. For example:

<outer_element>
    <internal_element>
    This tag is closed before the outer_element   
    </internal_element>
</outer_element>

Element
XML elements can be defined as building blocks of XML. Elements can appear as containers that hold text, elements, attributes, media objects, or any of these.

Every XML document contains one or more elements, whose scope is bounded by start and end tags, or an empty element tag to represent an empty element.

Syntax
The following is the syntax for writing an XML element:

<element-name attribute1 attribute2>
....content   
</element-name>

Here

element-name: Represents the name of the element. The names between the opening and closing tags must match.
attribute1, attribute2: It is the element attributes separated by spaces. Attributes define the properties of an element. It associates a name and a string value. Attributes are written in the following form:
name = "value"
Attribute_name_ is followed by an = sign and a string value wrapped in double quotes (" ") or single quotes (' ').

Empty element
The syntax of an empty element (an element with no content) is as follows:

b4ea431bf707e8b388cb43abd5651970
Here is an XML document using various XML elements:

<?xml version="1.0"?>
<contact-info>
    <address category="residence">
        <name>Tanmay Patil</name>
        <company>TutorialsPoint</company>
        <phone>(011) 123-4567</phone>
    <address/>
</contact-info>

XML Element Rules
XML elements need to follow the following rules:

Element_names can contain any alphanumeric characters. The only tag symbols allowed in names are hyphen (-), underscore (), and period (.).
Element names are case-sensitive. For example, Address, address and ADDRESS are different element names. The opening and closing tags of the
element must be the same.
An element is a container, which can contain text or elements, as you can see in the example above.

The above is the detailed content of A detailed introduction to the use of tags and elements in XML. For more information, please follow other related articles on the PHP Chinese website!