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packages/string_scanner/lib/src/utils.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library string_scanner.utils;
 
 /// Validates the arguments passed to [StringScanner.error].
 void validateErrorArgs(String string, Match match, int position, int length) {
   if (match != null && (position != null || length != null)) {
     throw new ArgumentError("Can't pass both match and position/length.");
@@ skipping 10 matching lines @@
 
   if (length != null && length < 0) {
     throw new RangeError("length must be greater than or equal to 0.");
   }
 
   if (position != null && length != null && position + length > string.length) {
     throw new RangeError("position plus length must not go beyond the end of "
         "the string.");
   }
 }