The local environment plan, called the omgevingsplan in Dutch, contains municipal rules for the physical environment. Location-specific provisions can be relevant to a building proposal. Consulting it is part of preparation rather than a substitute for every other assessment or permission.
How this term relates to your project
For an extension in Haarlem, the practical starting point is the address and the actual proposed design. Its location, use and relationship with the existing building may matter. An example elsewhere in the neighbourhood does not reliably establish the position for your plot. Use municipal information and the Omgevingsloket to investigate relevant rules and next steps.
Keep a record of the situation you checked, including the drawing used and questions raised with the municipality. If the proposal changes, earlier findings may need to be reviewed. Where interpretation is uncertain, ask how the provision applies to your specific proposal; a general explanation is not an individual decision about the project.