@Override
	protected void enterChannelsSpec(GrammarAST tree) {
		ErrorType errorType = g.isParser()
				? ErrorType.CHANNELS_BLOCK_IN_PARSER_GRAMMAR
				: g.isCombined()
				? ErrorType.CHANNELS_BLOCK_IN_COMBINED_GRAMMAR
				: null;
		if (errorType != null) {
			g.tool.errMgr.grammarError(errorType, g.fileName, tree.token);
		}
	}
Value of caseInsensitive option (false if not defined)
tool/src/org/antlr/v4/semantics/BasicSemanticChecks.java