The instant property isnan verifies the Not a Number (NAN) status of a float operand.

The read access to this property results in a boolean value false or true depending on whether the operand in context of which the property is evaluated does contain a valid floating point value or an invalid (Not a Number) value. Such invalid value can result from mathematical operations performed with incorrect arguments like the calculation of square root with a negative value. Please note, this property is read-only. The write access to this property is not allowed. For example:

See also the built-in function float_nan().