Why Browsers do not resolve simple known issues such as:
(in the context of CSS)
Do NOT start a class name with a number! This is only supported in Internet Explorer
Do NOT start an ID name with a number! It will not work in Mozilla/Firefox.
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These are not issues. This is the W3C standard.
Most good browsers try to follow standards as much as possible (Firefox, Chrome).
Some browser just doesn't care, or is trying to impose its own standard though (IE).