Some editors like Kate or Vim through the plugin YouCompleteMe (https://github.com/Valloric/YouCompleteMe) provide a generic code or text completion method by proposing words found in the current document as suggestions while typing. YouCompleteMe calls this identifier-based completion.

I find this feature quite useful because often strings are used in the own code which already appeared somewhere in the file and in Vim/Kate this technique allows a good completion experience even for languages which aren't currently supported. In Kdevelop, which uses the Kate component, the generic completer also increases the completion performance while editing C++ files as it kicks in much faster than the code model. Of course it should be possible to disable the generic completion engine in the settings.