The code you provided appears to be a **comment** rather...

The code you provided appears to be a comment rather than an actual piece of implementation. If this comment is attached to some code (not provided here), it likely refers to functionality or logic ensuring that a substring operation or query parsing process is robust and won't encounter errors ('choke') when dealing with special characters like &, ?, =, etc.

In general:

• Special characters like &, ?, and = are commonly used in URLs, query strings, or delimiters in data parsing. Properly handling these characters avoids issues like parsing errors or unexpected output.
• The "robust substring test" might involve code that safely extracts substrings or parses data without being disrupted by special characters.

To fully understand what the code does, please provide the actual implementation accompanying this comment.