code: public ContentAssistEntry createProposal(final String proposal, final ContentAssistContext context, final Procedure1<? super ContentAssistEntry> init) {
      return this.createProposal(proposal, context.getPrefix(), context, ContentAssistEntry.KIND_UNKNOWN, init);
    }
docs: Returns an entry with the given proposal and the prefix from the context, or null if the proposal is not valid.
  If it is valid, the initializer function is applied to it.