Lack of clear legislative frameworks can act as one of the major impediments to effective design and implementation of these policies, standing in the way of “positive urbanization.” Cities can adopt essential elements of laws that are grounded in sustainable processes and systems, and move on to more elaborated arrangements and legal instruments as management and governance institutions mature. They must be adapted to any country's and city’s specific needs, resources and capacities and be enacted according to specific circumstances. Since the 1990s, extensive research in many countries on urban regulations such as building codes, zoning, environmental rules, and others suggests that many urban regulations are out of date. Some reflected colonial heritage, others were biased in favour of middle- and upper-income groups, while others still generated perverse economic incentives for private (as opposed to public) investment in housing and other services.26 This goes to show that reform of urban regulations is an important lever for change.