Boolean Values

Boolean was named after an English mathematician of the 19th century called George Boolean who invented boolean values false( 0 ) and true( 1 ).
There are two types of Boolean Values:
i-Explicit Boolean Values
ii-Implicit Boolean Values

i-Explicit Boolean Values:
are two keywords TRUE and FALSE.

• They are case insensitive so you can write true, TRUE, TrUE.
• You cannot enclose them in quotes. ‘false’ is not allowed

ii-Implicit Boolean Values:
are referred to truthy and falsy values.

Falsy Values:

• Zero as a number or string e.g. 0, 0.0, ‘0’ are considered to be false.
• Any Empty String with nothing between the quotes ( ‘’, “” )
• An empty array.
• NULL( including unset values )
• simpleXML object created from empty tags .
• Everything else is true.

Truthy Values

• Any number apart from 0, 0.0 or ‘0’ is true ( even -1 is true )
• Any string within quotes (except empty quotes ) is considered to be true. Hence because ‘false’ is a string within quotes, it's considered to be true.