[1]
[CITE[X Sharp/Nodes]] ([TIME[2009-01-22 20:51:58 +09:00]] 版) <http://wiki.codeglide.com/X_Sharp/Nodes#The_in_operator>

[2] [CITE[Bug 623437 – Making an argument optional changes the order in which the method is enumerated]]
( ([TIME[2011-08-26 23:32:09 +09:00]] 版))
<https://bugzilla.mozilla.org/show_bug.cgi?id=623437>

[3] [CITE@en[623437 – Making an argument optional changes the order in which the method is enumerated]]
( ([TIME[2013-12-05 07:41:47 +09:00]] 版))
<https://bugzilla.mozilla.org/show_bug.cgi?id=623437>