Custom PHP function

NB! The Custom PHP function validator (in Field validation 7.x-1.x) has been replaced by the PHP code validator in version 7.x-2.x.

1. Click the link "Custom PHP function" to add a validation rule using php.
2. On "Add validation rule" form,Enter following info:
   Rule name: test Custom PHP
   Column:value
   Function name: mymodule_validate_myfield
   Custom error message: test Custom PHP error message.
3. Add mymodule_validate_myfield to one of your custom module file,such as mymodule.module,here is the example code:
   

   function mymodule_validate_myfield($variables){
   //drupal_set_message('123456');
     //a flag, TRUE means pass, FALSE means fail.
     $flag = TRUE;
   	//maybe what you need is the current value
     $value = $variables['value'];
   	//you could also access other variables as your need
   	//$item = $variables['item'];
   	//$delta = $variables['delta'];
   	//$items = $variables['items'];
   	//$rule = $variables['rule'];
   	//$langcode = $variables['langcode'];
   	//$entity = $variables['entity'];
   	
   	//Here add you validate logic,for example 
   	// $flag  = mymodule_validate_myfield_through_webservice($value);
   	if($value == 88){
   	  $flag = FALSE;
   	
   	}	
   	//return TRUE or FALSE
   	return $flag;
   }

   In this function, you should return TRUE,or FALSE. you could visit context variable through $variables, such as:
   $value = $variables['value'];

It is very simple.