Returns the zero-based index of the first occurrence of a IPlugin in the PluginCollection. 
PluginCollection. The zero-based index of the first occurrence of item in the entire PluginCollection, if found; otherwise, -1. 
Missing <remarks> documentation for M:log4net.Plugin.PluginCollection.IndexOf(log4net.Plugin.IPlugin)
PluginCollection Class | log4net.Plugin Namespace