Thinking about it some more, this is not correct since olddisplay is never set to "none" (it is set in hide()).
So since it cannot be "none", and if unset is set to "" in the current code, how can the subsequent style check result in "none"?
Okay, the creation of a temporary element is clear to me, to find out what the default value of "display" is for the given tag if none is given. What is not clear to me now is how we ever get there, since as I read the code that code is executed only if setting style.display="" results in it becoming "none" when reading the property afterwards?
BREAK... more issues (is it me or the code?)
Reading hide() I'm even more confused: what does
if ( !old && old !== "none" )
mean? The second part old!==="none" is reached only if old does not exist??? (not a truthy value)