What is XML?


What is XML?

When most people come across the term XML, they often confuse it with HTML. Though it is true there are some similarities between XML and HTML, they differ in functionalities. So as programmers, you ought to know what exactly XML is and how it is used in programming. Here is a detailed guide that can help you fully comprehend what XML is. 

What Does XML Stand For?

XML is an abbreviation for eXtensible Markup Language. The World Wide Web Consortium (W3C) created a dynamic form of language used in building web pages. Its role is to transport data rather than display it. One of the key reasons it stands out from other programming languages is its syntax.

Every programming language has its own predefined syntax. You may guess that XML is also the same, but no. For XML, the form of syntax is in the hands of the programmers. Through tags, programmers can define the syntax for encoding documents that both humans and machines could decipher.

The syntax is created through tags, which define the document’s structure and the location on where the document should be transported and stored. In this article, we will look at the following areas of XML:

  • Hierarchy
  • Declaration
  • Syntax
  • Tags and Elements
  • Tags and Elements Rules
  • XML vs HTML


Each instance of an XML tag is referred to as an element. Components in an XML file are organised in layers of hierarchy, meaning elements can contain other elements within them.

The topmost element in the hierarchy is referred to as the “root” element, and it contains all other elements, which are referred to as “child” elements.


Below is how an XML program is declared initially:

<?xml version = "1.0" encoding = "UTF-8"?>

Where version denotes the XML version, and encoding specifies the character encoding used in the document. Here UTF-8 is used, which is the common choice of encoding used in web pages and browsers.


Below is the basic XML syntax.

<?xml version = "1.0" encoding = "UTF-8" ?>


  • The root refers to the topmost element.
  • The child refers to the elements that are engulfed within the root.
  • And subchild relates to the elements engulfed within the child tags.

Syntax Rules for XML Declaration

  • The first statement in the XML document must be the XML declaration.
  • The XML declaration must begin with “?xml>,” with “xml” typed in lower case.
  • An HTTP protocol can override the value of encoding that you specify in the XML declaration.

Tags and Elements

Except for declarations, XML Tags and Elements Tags work in tandem. An opening tag and a closing tag make up every tag pair.

The tag names are indicated using the <> symbols.

When using a tag, make sure the start and end tags are identical, except that the closing tag comes with an / after the < symbol.



The space between the opening and closing tags is where developers will add the content.

An element in XML is the combination of opening tag, content and closing tag.

If the tags don’t contain content within them, they are referred to as empty tags:


Tag and Element Rules 

Here are some XML tag and element rules programmers should look out for:

  • Case of the letters matters when it comes to tags.
  • A single root element is required in all XML documents.
  • closing tag is required for all elements, except for declarations.
  • The tag’s name must start with a letter or an underscore, and it cannot begin with XML.
  • Letters, numerals, hyphens, underscores, and periods can all be used in a tag name. The only punctuation marks allowed are underscores and periods.
  • There shouldn’t be any spaces in a tag name.
  • All elements must be appropriately nested.


Since XML has the term Markup Language in its name, it’s natural for people to mix it up with HTML. Though HTML and XML are relatively similar in that they are both involved in developing web pages and using tags, they are not quite the same. For example, unlike XML, HTML has standardised symbols and syntax.

Another contrary factor that distinguishes it from HTML is that HTML mainly focuses on presenting the content to users. In contrast, XML is used to carry out processes on data.

If you are still confused between HTML and XML, here are some more distinctive features between both languages:

  • XML is dynamic since it is used in the transport of data, while HTML is static since it focuses on the display of data.
  • It is case sensitive, while programmers can write HTML codes in any case.
  • In XML, it is mandatory to use closing tags, while in HTML, closing tags are not that important.
  • In XML, even minor errors impact the final result, but slight typos in HTML are ignored.

With the above-listed differences, you now might have gotten a gist of the difference between HTML and XML.

What is XML Used For?

According to the World Wide Web Consortium(W3C), XML’s main objective is to create a “simple text-based format for representing structured information”. The most common application of XML is to

  • Simplify the creation of HTML documents for a large website.
  • Exchange the information between organisations and systems.
  • Unload and reload the databases.
  • Store and arrange the data to customise your data handling needs. 
  • Merge with style sheets to create almost any desired output.

Now that you know what XML is used for, here are some real-world examples to help novice developers grasp it.

In Web Searching

Have you ever wondered how search engines function to deliver the most relevant results?

In HTML, there are meta tags that contain a brief description of the web pages. Then, the search algorithm merges the query with the given description, and the right results are brought to use.

However, XML does this function better than HTML.

For example, you are searching for the works of a celebrity, you will get results like the latest news, interviews etc., this is using HTML. Using XML, the search engine will restrict the search to only the celebrity’s works.

In Web Pages and Applications

The content for web apps and pages are pulled from XML files, and this is because HTML and XML work closely together.

In Transporting Digital Information

XML files are highly transportable due to their text-based format and are thus commonly used for transporting data between web servers. For example, SOAP APIs and REST APIs send data to other applications in the form of XML files.

Computer Applications

XML files make it simple for computer software to organise and retrieve data. After retrieving it from the file, programs can determine what to do with the data. This could include storing it in a different database, incorporating it into the program’s backend, or presenting it on the screen.

XML is also used to create various ubiquitous file formats. Consider the following file extensions:

  • .docx (for Word documents),
  • .xlsx (for Excel spreadsheets), 
  • .pptx (for PowerPoint presentations) 

The ‘x’ at the end refers to XML.

XML code modules may also appear within an HTML file to assist in displaying content on the page. As a result, XML is particularly well suited for building interactive websites and pages with dynamically changing content. 

An HTML file might select to display only particular components in the XML code based on the user or screen resolution, offering visitors a personalised browsing experience.

What Is an XML File?

The file extension “.xml” indicates that an XML file contains XML code. It includes tags that specify how the document should be organised and how it should be saved and transmitted over the internet.

What Is an XML File Used For?

XML files are plain text documents that are effortless for computers and humans to produce, store, transfer, and interpret. As a result, it is one of the most widely used languages on the internet. 

In addition, many web-based software applications use it to store and deliver data to other applications.

How to Create an XML File?

Let’s look into how to create an XML file:

  • Open your preferred text editor.
  • Write an XML declaration on the first line.
  • Place your root element beneath the declaration.
  • Insert your child elements inside the root element.
  • Inspect your file for errors.
  • Use the .xml file extension to save your file.

You can test your file by opening it in the browser window.

How to View and Edit an XML File?

Since XML files are text files, programmers can access them in various ways. For example, if you only need to read XML files occasionally, you can open them in your preferred browser. Or, you can use an online XML editor or a text editor on your computer if you often examine, edit, and reformat XML files.

Using a Web Browser to Open XML Files

Users can view XML files directly in the browser window in all modern web browsers. You can select an XML file from your device and choose to open it with your web browser. For example, let us use google chrome as the browser.

  • Use google chrome browser to open the XML file.
  • While the text will display differently depending on the browser, you should be able to quickly analyse the file’s contents and possibly conceal and reveal specific several elements.
  • If there is an error in the file, your browser will display an error message.
  • It’s worth noting that you won’t be able to edit the file this way in your browser. For editing, you’ll need a specialised tool to change the file.

Using an Online XML Editor to Open XML Files

You can use an online text file editor to view your XML files, alter their contents, or convert them to other file types.

  • Click Browse in the tool to upload a file from your computer. Once uploaded, you can inspect and modify the XML content hierarchy on the right.
  • When you’re done editing, click Save & Share to save the new XML file.

Using a Text Editor to Open XML Files

Programmers can open XML files with any text editor like any other text file. However, common editors, such as Notepad and Word, are so old-fashioned and are unlikely to show your XML files with colours or indentation. 

To understand the code better, programmers should opt for a professional text editor that can recognise the.xml format and show your files appropriately. Notepad++, Xmplify, and Eclipse are popular options. With professional text editors, code indentations and menial errors are resolved on their own, so it is best to work on XML through proper software.

Pros and Cons of XML

Like any other coding language, XML also comes with its own share of pros and cons; here are some important ones.


  • It is a platform-independent language. So users can run it on any system regardless of the operating system type.
  • Because it employs human vocabulary rather than sophisticated technical jargon, it is simple to read and comprehend.
  • Unicode is an international encoding standard for compatibility with various languages and scripts in which each letter, digit, or symbol is allocated a unique numeric value that is applicable across platforms and software.
  • XML and Java are pretty compatible.
  • It uses DTD and schema validation to verify that the XML document is void of errors.
  • Thanks to its cross-platform nature, the XML codes do not need any conversion and can be easily shared between various systems.


  • The syntax is overly complicated and redundant.
  • The syntax consumes too much storage space due to its redundancy.
  • Arrays are not supported.
  • Despite its use as a backend language, it lacks rendering instructions.
  • Since no browser understands it, programmers must first translate it to HTML code.


XML may sound like bad news for programmers of all levels. However, as daunting as it initially appears, XML is a convenient tool for web developers who want to write high-quality code in terms of functionality, security, and performance. Invest time in practice, just like any other programming language, while learning XML to master it rapidly.

Coding basics for free

If you want to see what it’s like to code, we host a free coding challenge that will show you what it is like to use our world-class LMS. After one hour a day over five days, you will learn how to build your first webpage. On this short, free course, you will learn the basics of HTMLCSS and JavaScript. Register now through the form below this article. 

Coding the Future: Developer Spotlight - Sian C.

In October 2022, Sian C. joined Code Institute’s Level 5 Diploma in Web Application Development programme, which is run in association with Cardiff and Vale College and is funded via the Welsh Government’s Personal Learning Accounts (PLA) initiative. The course aims to equip learners with full-stack software development skills, preparing them to enter the digital […]

Coding the Future: Developer Spotlight - Nathan Parsley

In May 2023, Nathan Parsley joined the Level 5 Diploma in Web Application Development programme, delivered at East Kent College Group (Ashford) by Rachel Furlong using the Code Institute learning platform. The course equips learners with full-stack software development skills, preparing them to enter the digital workforce in various roles. Nathan has completed the programme […]

Coding the Future: Developer Spotlight - Wendy Bovill

In March 2023, Wendy Bovill joined the Level 5 Diploma in Web Application Development programme, which is delivered at Westminster Adult Education Service (WAES) using the Code Institute learning platform. The course equips learners with full-stack software development skills, making them ready to enter the digital workforce in various roles. Digital Academy leader Candice Fanning […]