Validating a page

If you're creating a sheet that requires users to enter data, you might want to restrict entry to a certain range of dates or numbers, or make sure that only positive whole numbers are entered.

Excel can restrict data entry to certain cells by using data validation, prompt users to enter valid data when a cell is selected, and display an error message when a user enters invalid data.

That might have been the case a decade ago, when validation was the tool of choice of people more interested in harnessing the power of the markup languages than creating beautiful designs for their content; when many designers were not taught basics of Web technology and would create beautiful but fragile and unreliable web sites. In the past decade, most of the stunning, content and design-rich Web sites were built with standard (X)HTML, CSS and scripting.

This article was co-authored by Paul Chernyak, LPC.

In the past, many authors who relied on the quirks of Netscape 1.1 suddenly found their pages appeared totally blank in Netscape 2.0.

Whilst Internet Explorer initially set out to be bug-compatible with Netscape, it too has moved towards standards compliance in later releases.

Creating Web pages or applications according to a widely accepted coding style makes them easier to maintain, even if the maintenance and evolution is performed by someone else.

Many professionals have been authoring the Web with HTML and CSS for years and know these technologies by heart.

Indeed, most developers creating rich Web applications know that reliable scripting needs the document to be parsed by User-Agents without any unexpected error, and will make sure that their markup and CSS is validated before creating a rich interactive layer.

It is indeed one of the principal strengths of the web, that (for example) a visually impaired user can select very large print or text-to-speech without a publisher having to go to the trouble and expense of preparing a separate edition.

Do remember: household-name companies expect people to visit afford that luxury?

Validation is one of the simplest ways to check whether a page is built in accordance with Web standards, and provides one of the most reliable guarantee that future Web platforms will handle it as designed.

It is reasonable to consider that standards such as HTML and CSS are a form of “coding style” which is globally agreed upon.

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