Implements a factory for runtime type checkers (shape, arrayOf, oneOf, instanceOf, etc.) similar to React PropTypes. Each checker generates a validation function that returns null or an error. The module is self-contained, takes no dependencies on other san internals, and can be extracted as a standalone validation library for any JavaScript application that needs declarative, performant runtime type checking.

Provides a nextTick function that queues a callback to run after the current synchronous batch, using the fastest available mechanism (setImmediate, MessageChannel, Promise, fallback to setTimeout). This pattern is essential for frameworks that need deferred rendering and batch updates. The implementation is self-contained, handles edge cases (message channel with port2, promise rejection), and can be reused directly in any project requiring a reliable deferred execution primitive.

A small but well-crafted string scanning utility (Walker class) that tracks a position within a source string and provides methods to read characters, skip whitespace, expect specific sequences, and manage position markers. It is used by the template parser to tokenize attributes, directives, and expressions. The pattern is generic and can be extracted for any custom parser or lexer implementation, demonstrating clear separation of scanning logic.