[KennyMcSimpson]

The slice parser currently accepts multiple numbers in the same component and silently keeps only the last one. For example, jmespath.search('[0:1 3]', list(range(6))) returns [0, 1, 2], treating the expression as [0:3]. [0:1-2] and [::1 2] are accepted similarly.

The slice grammar permits at most one number in each component. Reject a second number through the existing syntax-error path instead of overwriting the component. Checking against None also correctly rejects repeated numbers when the previous number is zero.

Add eight invalid-syntax compliance cases covering repeated end/step values, signed values, zero values, and both field and root slices. Add valid whitespace and zero-endpoint controls, and update the changelog.

Validation on Windows / Python 3.13:

• Before the fix: all eight new syntax cases fail because the invalid expressions parse successfully; the other 991 tests pass, with one existing skip.
• python -m tox -e py313: 1001 passed, 1 skipped.
• With the exact pinned CI dependencies and CI coverage command: 1001 passed, 1 skipped, 99% total coverage.
• Directly verified all eight invalid expressions raise ParseError at the second number.

Other Python versions and operating systems are left to CI. This contribution was prepared with AI assistance.