Converts each element to a String and concatenates the strings.
Iterates through elements of this iterable, converts each one to a String by calling Object.toString, and then concatenates the strings, with the separator
string interleaved between the elements.
String join([String separator = ""]) => readClasses().join(separator);
© 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
https://api.dart.dev/stable/2.5.0/dart-svg/AttributeClassSet/join.html