HTML Doctype Explained
An HTML doctype is used as the first element in the source code of web pages. This element should never miss in all HTML documents. However, doctype is usually forgotten, and many webmasters either forget its importance or do not know its function at all. Again, some webmasters do not feel the need to have the element in all their web pages.
Doctype element was not always there when HTML was first developed. The element specifies the version for HTML used on a web page. It also gives more details about elements and properties on an HTML code. With a doctype element, browsers can process the source code and display a web page correctly. It is standard practice to have a doctype element in the source code of all web page documents. If the element is not in the source code, this is seen as an error even when the text is displayed right. The tools used to check the source code will show an error when the doctype element misses in an HTML document.
Where is Doctype Used?
Doctype element appears in the HTML code before the actual HTML code, even before the HTML tag. It needs to appear in the source code of individual web pages – using it on the homepage alone is not sufficient. Don't use plagiarised sources.Get your custom essay just from $11/page
It is also used in XML documents and SVG Graphics.
Different Doctypes Used
The earlier versions of HTML and XHTML 1.01 and 1.1, doctypes were long and complex. Then, the doctype element could only be copied and pasted into the source code even by webmasters who know how to code. In the earlier versions of HTML, the doctypes below had to be used:
HTML 4.01 – Strict, which looks like:
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.01//EN” “http://www.w3.org/TR/html4/strict.dtd”>
This is an exact and very strict code if you compare it to XHTML. The elements in Strict have to be closed.
HTML 4.01 – Transitional:
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.01 Transitional//EN “http://www.w3.org/TR/html4/loose.dtd”>
Unlike Strict, Transitional is more tolerant and less strict. It is more comparable to HTML 5.
In HTML 4 and earlier versions, which are based on SGML, the document type definition (DTD) needs specification in the doctype element of these versions. The description shows the rules and elements and also includes other properties in the code of a document to facilitate the correct display of a page in web browsers.
SGML is short for Standard Generalized Markup Language, and it is the obsolete version that came before HTML. After HTML 5 was introduced, the source code ceased to fall under SGML due to compatibility issues.
Doctype elements in HTML 1.0 and 1.1 look like shown below:
XHTML 1.0 – Strict looks like:
<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Strict//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd”>
XHTML 1.0 – Transitional appears as:
<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Loose//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-loose.dtd”>
XHTML 1.1 Strict appears:
<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”>
Like in HTML 4 and earlier versions of HTML, the doctype definition needs to be specified given that XHTML1 and 1.1 are based on SGML. Browsers will, therefore, rely on the information and instructions on the source code to correctly display a web page. In this case, both Strict and Transitional carry the same meaning as in HTML 4.0 and 4.1 – they show the rules that apply to a document’s source code markup.
With the introduction of HTML5, the doctype element has changed significantly. HTML5 is not based on SGML. Again, the use of the doctype is now less complicated. The doctype element is only as follows:
<!DOCTYPE html>
The simple element above is enough without extra rules or links. As simple as the element is, it gives browsers all the information they need to display a web page correctly. With HTML 5, therefore, webmasters have one less programming aspect to worry about.
Missing Doctype Element and Associated Problems
If a doctype element is missing in the source code of a web document, a web page may not be displayed correctly. In most cases, however, the page will still be displayed correctly, especially if the general code of the page is written in HTML5.
If the general code of a page is written in other versions of HTML and not HTML5, or it uses functions that need a doctype definition in advance, there may be errors in the display of a page or unexpected problems might occur.
Summary
For any website, the doctype element is an essential part of the source code. When placed at the beginning of the source code, even before the HTML tag, it ensures a web page is displayed correctly. Also, though a web page might still be displayed correctly without the doctype element, it should not be forgotten. With HTML 5, the element has been simplified with fewer rules and links to worry about.