HTML is hypertext which is nonlinear navigation between related or unrelated documents, ie. links, and markup language with is symbols (in web speak, tags) to indicated to the printer (in web speak, browser) how the content should look and be presented.
The term markup is derived from the traditional publishing practice of “marking up” a manuscript, that is, adding symbolic printer’s instructions in the margins of a paper manuscript. For centuries, this task was done by specialists known as “markup men” and proofreaders who marked up text to indicate what typeface, style, and size should be applied to each part, and then handed off the manuscript to someone else for the tedious task of typesetting by hand. A familiar example of manual markup symbols still in use is proofreader’s marks, which are a subset of larger vocabularies of handwritten markup symbols. [Source]
As bloggers, we tend to write quickly and proof later (yes I generalize but you will see this post on my first draft). The array of blogging tools out there provide handy little WYSIWYG editors to help rush content out. Personally, I disable WordPress’s wysiwyg. These tools allow us to be sloppy and produce bad code/markup. The W3C is an international member organization with the mission of creating Web standards and guidelines. The W3C does not define the World Wide Web but because Tim Berners-Lee, who is credited with inventing the Word Wide Web in 1989 while working for CERN, also created the W3C, and so many industry experts are part of the consortium, W3C recommendations are highly regarded.
The W3C provides tools to validate your markup against the HTML specification. By making sure your website, and a blog is just a website that updates often, has valid HTML you can be assured that page will present its information in most any browser or news reader as you want the person reading it to see it. Non-valid markup can send a browser into quirks mode and the outcome may be unpredictable. Valid markup also lends to more favorable search engine placement. A blogger who takes the time to make sure their site template is valid HTML and that their regular posts are valid HTML making the entire site valid HTML may get higher placement in a search engine than a comparable blogger who does not validate.
That said, there is an argument that validation for bloggers may not be all that important. According to Bug Leak, all the blogs in Technorati’s Top 20 fail to validate.
This probably means that complying to the W3C standards is not a priority for the most popular content creators on the planet. [Source]
The article lists these 20 blogs and the number of validation failures. I was curious to find out what separates these great content creators from RealityMe (of course, I can guess that they have focused topics, thousands of links in, huge readership, more regular posting, etc.) so I added each to my feed reader to gander daily for a bit. I have saved the RSS links as OPML so that anyone can import the same 20 blogs into their readers. Bug Leak points to a great tool for WordPress users called XHTML Validator plugin. This plugin checks the content going into the database (not the actual template) to make sure that your posts are valid. How does one write valid code without knowing what constitutes valid HTML? Simply install the XHTML Validator plugin and begin posting. When it shows you errors, correct them and learn by doing!