docs: private void validateExpr(SqlNode expr, SqlValidatorScope scope) {
  		if (expr instanceof SqlCall) {
  			final SqlOperator op = ((SqlCall) expr).getOperator();
  			if (op.isAggregator() && op.requiresOver()) {
  				throw newValidationError(expr,
  					RESOURCE.absentOverClause());
  			}
  		}
  
  		// Call on the expression to validate itself.
  		expr.validateExpr(this, scope);
  
  		// Perform any validation specific to the scope. For example, an
  		// aggregating scope requires that expressions are valid aggregations.
  		scope.validateExpr(expr);
  	}