code: function after(args) {
      const source = args.source;
      const index = args.index;
      const err = args.err;
      const errTarget = args.errTarget;
      const lineCheckStr = args.lineCheckStr;
      const onlyOneChar =
        args.onlyOneChar === undefined ? false : args.onlyOneChar;
  
      activeArgs = { source, index, err, errTarget, onlyOneChar };
  
      switch (expectation) {
        case "always":
          expectAfter();
          break;
        case "never":
          rejectAfter();
          break;
        case "always-single-line":
          if (!isSingleLineString(lineCheckStr || source)) {
            return;
          }
  
          expectAfter(messages.expectedAfterSingleLine);
          break;
        case "never-single-line":
          if (!isSingleLineString(lineCheckStr || source)) {
            return;
          }
  
          rejectAfter(messages.rejectedAfterSingleLine);
          break;
        case "always-multi-line":
          if (isSingleLineString(lineCheckStr || source)) {
            return;
          }
  
          expectAfter(messages.expectedAfterMultiLine);
          break;
        case "never-multi-line":
          if (isSingleLineString(lineCheckStr || source)) {
            return;
          }
  
          rejectAfter(messages.rejectedAfterMultiLine);
          break;
        default:
          throw configurationError(`Unknown expectation "${expectation}"`);
      }
    }
docs: Check for whitespace *after* a character.
  
  Parameters are pretty much the same as for `before()`, above, just substitute
  the word "after" for "before".