Add initial implementation

[marcospassos]

Summary

Add initial implementation.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings

[marcospassos]

@renan628, regarding your comment: the expected behavior is to return null whenever something does not match, so the original content is used instead. These are treated as unexpected cases that should never happen. This is basically a port of JS code.

[denis-rossati]

Appart from the existing comments, lgtm