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replaceFirst abstract method
String replaceFirst(Returns a new string in which the first occurrence of from in this string is replaced with to, starting from startIndex:
'0.0001'.replaceFirst(new RegExp(r'0'), ''); // '.0001'
'0.0001'.replaceFirst(new RegExp(r'0'), '7', 1); // '0.7001'
  Source
String replaceFirst(Pattern from, String to, [int startIndex = 0]);
  © 2012 the Dart project authors
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 https://api.dartlang.org/stable/1.24.3/dart-core/String/replaceFirst.html