Improve ERROR.CONVENTIONS

ERROR.CONVENTIONS

@@ -81,3 +81,35 @@ ICU operates, where functions return immediately if an error is set.
 Error resetting can be done with:
 void intl_error_reset(NULL TSRMLS_DC);				/* reset global error */
 void intl_errors_reset(intl_error* err TSRMLS_DC );	/* reset global and object error */
+
+In practice, intl_errors_reset() is not used because most classes have also
+plain functions mapped to the same internal functions as their instance methods.
+Fetching of the object is done with zend_parse_method_parameters() instead of
+directly using getThis(). Therefore, no reference to object is obtained until
+the arguments are fully parsed. Without a reference to the object, there's no
+way to reset the object's internal error code. Instead, resetting of the
+object's internal error code is done upon fetching the object from its zval.
+
+Example:
+U_CFUNC PHP_FUNCTION(breakiter_set_text)
+{
+	/* ... variable declations ... */
+	BREAKITER_METHOD_INIT_VARS;			/* macro also resets global error */
+	object = getThis();
+
+	if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "s",
+			&text, &text_len) == FAILURE) {
+		intl_error_set(NULL, U_ILLEGAL_ARGUMENT_ERROR,
+			"breakiter_set_text: bad arguments", 0 TSRMLS_CC);
+		RETURN_FALSE;
+	}
+
+	/* ... */
+
+	BREAKITER_METHOD_FETCH_OBJECT;		/* macro also resets object's error */
+
+	/* ... */
+}
+
+Implementations of ::getErrorCode() and ::getErrorMessage() should not reset the
+object's error code.