function addBinding ($prop, Expression $bindExp)
  {
    if (!isset($this->bindings))
      $this->bindings = [];
    $this->bindings[$prop] = $bindExp;
  }
function addBinding ($prop, Expression $bindExp)
  {
    if (!isset($this->bindings))
      $this->bindings = [];
    $this->bindings[$prop] = $bindExp;
  }
function addBinding ( $ prop , Expression $ bindExp ) { if ( ! isset ( $ this -> bindings ) ) $ this -> bindings = [ ] ; $ this -> bindings [ $ prop ] = $ bindExp ; }
Registers a data binding.

@param string     $prop    The name of the bound property.
@param Expression $bindExp The binding expression.
Registers a data binding .