P{text-indent:none/normal/0;}

Question

in css i saw many property with value 0 or none .w why they even put it

Answer 1

You can encounter some other special keywords, as 'unset', 'inherit'... but only some are expected ( valid ) value, depending on which element/property you try to apply it ^^ ( see references to know authorized values )

Answer 2

To set it hidden(none)
or like as this
border-radius:100% 0 100% 100% (0)
or
used for Animation (normal)