function focus(elem) {
		if ( elem ) {
			elem.focus();
		}
	}
Set position of the Callout window relative to the parent control.
This function automatically calculates and sets the correct offset,
use it instead of <code>setMyPosition/setAtPosition</code>.
@param {sap.ui.core.Dock} myPosition docking position of the Callout
@param {sap.ui.core.Dock} atPosition docking position of the parent control
@return {this} <code>this</code> to allow method chaining
@public