function bind ($prop, $expression)
  {
    $this->bindings[$prop] = $expression instanceof Expression ? $expression : new Expression($expression);
  }
function bind ($prop, $expression)
  {
    $this->bindings[$prop] = $expression instanceof Expression ? $expression : new Expression($expression);
  }
function bind ( $ prop , $ expression ) { $ this -> bindings [ $ prop ] = $ expression instanceof Expression ? $ expression : new Expression ( $ expression ) ; }
Binds a property to a databinding expression.

@param string              $prop       A property name.
@param Expression[]|string $expression If a string is given, it will be converted to an {@see Expression} instance.
Binds a property to a databinding expression .