# LiveCode Builder Language

## Replace concept of 'undefined' with 'nothing'

* The use of the keyword 'undefined' is now deprecated, 'nothing' should be used instead.
  * Use 'returns nothing' to indicate a handler which returns no value.
  * Use 'nothing' to indicate no value when manipulating optionally type variables
* The 'is defined', 'is undefined', 'is not defined', 'is not undefined' syntax is now deprecated, 'is' and 'is not' should be used with 'nothing' instead
  * Use `<expr> is nothing` and `<expr> is not nothing` to test whether an expression has a value or not
  * The phrase `<left> is <right>` will now return true if `<left>` and `<right>` are both nothing
  * The phrase `<left> is not <right>` will now return true if one of `<left>` or `<right>` are nothing (but not both).

