I would add that the term "by-laws" is a litte confusing.
If you will consider 501c3 Non Profit Staus, the IRS does not consider "by-laws" by themselves to be enough to apply. They require "Articles of Organization" which are like "by-laws" but have additional requirements.
However, "by-laws" are the common term for a controlling document that describes how an organization - like a PTO - operates (membership, voting rights, board members/duties, committees) AND has been approved by the membership of the org. As Crew Chief said, they are structured, but not overly detailed. As guiding principles for the org., they should be difficult to change (supermajority).
Often, underneath the controlling document are a more detailed set of rules/procedures that describe in more detail how the organization runs. These should be easier to change (simple majority) as theyt would often need to adjust to changing conditions.
I can offer how my team views the two different documents:
By-Laws are a more structured document outlining voting procedures, officers' duties, term lengths, elections, membership requirements, reporting structure, and so on. They are the types of 'constants' that your group need to maintain and a very ivolved process is required to alter them.
Standing Rules, or what we call Policies and Procedures, are the types of things that can change frequently and are not so serious that they require a voting process to change. Our document covers things such as how/where to sign in and out of the building, which copiers to use, what times of day to avoid using equipment or the teachers' lounges and workrooms, which mailboxes to use... They are still rules that you expect members will follow while conducting their day-to-day business so the document should be taken seriously.
Some people come into our lives and quickly go. Some stay for awhile and leave footprints on our hearts. And we are never, ever the same."
"The ultimate aim of karate lies not in victory or defeat but in the true perfection of one's character."