0446Name_Not_Found
2018/02/12(月) 18:41:39.12ID:mE+yTOziThe attribute value can remain unquoted
if it doesn't contain spaces or
any of " ' ` = < or > .
Otherwise, it has to be quoted using either single
or double quotes.
The value, along with the = character,
can be omitted altogether
if the value is the empty string.
だそうな