Learning Method
We can learn by running our pages through the W3C validator. (The W3C CSS validator is more sensitive and emphatic about these things, more so than the XHTML validator.)
The W3C validator will alert us if we have used a non-standard reference or if we have errored in the construction of an entity. The validator will also tell us if a character requires one. A character that does not strictly require one today, might require one tomorrow, because changes are so rapid in this field of endeavor.
