Regular Expressions and Input Validation Questions

Techniques for validating and parsing input safely and performing pattern based extraction using regular expressions. Areas include designing white list validation and canonicalization pipelines, escaping and sanitization for different contexts, defending against Regular Expression Denial of Service by avoiding catastrophic backtracking, input size and type limits, multi layer validation strategies, using parsing libraries instead of fragile patterns for complex formats, and test driven validation. Interviews focus on when to use regular expressions, performance and security risks, and how to safely validate inputs from untrusted sources.