Tonight is one of those nights at Lawrence City Hall where people may come to appreciate the importance of technicalities.

There’s an item on the City Commission’s agenda that looks pretty technical because it involves a lot of language about development codes, definitions and other terms of art that make the hearts of city planners everywhere swoon.

There’s no denying there is plenty of technical stuff to wade through here, but really, city commissioners will be talking about an issue that often pits neighborhoods against landlords: How many people can live in a house in Lawrence?

The general rule for several years now has been that no more than three unrelated people can live in a single-family home, and no more than four unrelated people can live in a multifamily apartment and such.

But the key word in the phrase “general rule” is “general.” As the mayor recently found out, there are plenty of neighborhoods in Lawrence where more than three unrelated people can legally live in a single family home or duplex.

That’s because there are plenty of single-family homes or duplexes that are built on land not zoned for single-family or duplex construction.

In very simple form, the City Commission tonight will consider new rules that will take about 3,000 of those homes that currently can legally have four unrelated people living in them and reduce that number to no more than three unrelated people in them.

If approved, landlords will soon find out how a technicality can technically hit them in the wallet.

On the flip side, neighbors may find out how a few word changes can help reduce issues of overcrowding in their neighborhoods.

Which neighborhoods are we talking about? Well, for one, the west Lawrence neighborhood the mayor lives in. He discovered the vagaries of the city code when he realized there were more than three unrelated people living in a home across the street from his house on St. Andrews Drive.

But you are perhaps looking for more specifics than that. So, grab some toothpicks and prop those eyelids open. We are about to discuss the not-so-exciting world of zoning.

If you live in a neighborhood that falls into what I call the category of ‘P’ zoning, you will want to pay attention. (Gentlemen, you also don’t want to get confused about what rights ‘P’ zoning gives when you are faced with a full bladder and a long line at the restroom. It is not a defense that holds up in court.)

What I call P zoning are categories the city calls Planned Unit Developments, Planned Residential Developments, Planned Commercial Developments, Planned Industrial Developments and Planned Office Developments. Those are all specific zoning types in the city, and all of them technically allow for some residential development to occur.

The way the city code is written currently, any residential development in those P zoning categories can have up to four unrelated people. This gets confusing to neighbors because the houses often look like any other single-family house or duplex in the city, which are limited to three unrelated people. But it is the zoning of the land that dictates the rules that the house must follow.

The rule change up for discussion at tonight’s meeting would make it clear that single-family homes and duplexes in those P zoning categories would be limited to no more than three unrelated people.

A new city report estimates there are about 2,700 such homes in the P zoning districts that would be affected by the change. How many of them are rentals isn’t known, but I suspect the number is fairly large.

A few other zoning categories also would be affected. They include commercial and industrially zoned properties, which occasionally have homes built on them.

One category that is not included is the RM district, which is a type of multifamily zoning category. There are single-family style homes and duplexes built on that type of zoning, however. The Oread neighborhood is a good example of an area that has several homes that are on RM zoned property.

City staff members are not proposing that homes with RM zoning be included in the rule change. But a few residents of the Oread neighborhood are asking the City Commission to consider such a change. That would be a big one. The city estimates there are about another 4,000 units that may be affected by the rule change, if the RM district were included.

The discussion tonight is just the beginning of the process. If the city decides to move forward the Planning Commission will also have to debate the item. But if you are a landlord or a resident who lives in an area with a lot of rentals, it might be a debate worth watching. The City Commission meets at 6:35 p.m. today at City Hall. You’ll have to bring your own toothpicks, though.