This came up before: https://lists.webkit.org/pipermail/webkit-dev/2010-May/012873.html but I'd like to understand it a bit better. It feels there were two points of view: 1. Use explicit only when necessary to prevent an undesirable implicit conversion like int to vector. 2. Use explicit except when it is desirable to allow an implicit conversion that makes the code simpler. For example, the String <-> AtomicString makes the bindings generator code simpler since it doesn't need to know which the underlying method takes. Are there any reasons beyond personal preference to select either of these? Starting list: Pro's for #1 It is a pain to remember to put explicit every time you have a constructor with one argument. Pro's for #2 It would prevent accidental mistakes that happen with implicit constructors. dave