code: public static String getCoreValueExpression(UIComponent component) {
  		ValueExpression valueExpression = component.getValueExpression("value");
  		if (null != valueExpression) {
  			String v = valueExpression.getExpressionString();
  			if (null != v) {
  				Matcher matcher = EL_EXPRESSION.matcher(v);
  				if (matcher.find()) {
  					String exp = matcher.group();
  					return exp.substring(2, exp.length() - 1);
  				}
  				return v;
  			}
  		}
  		return null;
  	}
docs: Return the core value expression of a specified component
  
  @param component
  @return