Single vs Double Quotations


When do you use "double quotations" and when do you use 'single quotations'?
Are they interchangeable?


It is conventional to always use double quotes until otherwise specified. They are usually interchangeable without error, but always use double quotes if not specified.


In javascript, for example, you use single quotation inside of a double quotation for convenience.
For example:

windows.alert("He said: 'hello'")

or you could just write

windows.alert("He said: \"hello\"")

On top of everything. Single and double quotations are interchangeable. But it would be better to use double quotation.