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Custom tags… why not?
why is using custom tags in HTML a bad practice?
code here: http://jsfiddle.net/ZXr2L/1/ works just fine with browsers.
if i have to style a 100 random words on a webpage, using <hg></hg> would save lot of space and data instead of using <span class="hg"></span> . CSS also works fine with these custom tags. Only issue would be W3 HTML validity.
You answered your own question.
Are you working in a compnay where someone else may need to work with your code in the future? Can you be certain that future browsers are going to be ok with your custom tags? Can you be sure that older browsers will handle them?
Standards can obviously be broken, and if you want to do things your own way then you can. However, standards are just that – STANDARDS. Adhering to them can save you problems when things do not work and will ensure your code is the highest quality it can be.