Certain types of behavior ultimately come down to a handful of rule tables in the database. The goal of both the circ scripts and the alternative matrix tables is to pick rows from those rule tables. In older versions of Evergreen, you would configure these tables with the "Open-ILS Bootstrapping Scripts", under "Circulation and Holds Rules". This interface lives by default at http://localhost/cgi-bin/config.cgi (if you use a browser on the Evergreen server itself. Otherwise, you will need to tweak your Apache config to allow external access to those scripts and modify your URL as appropriate.) You could also manage these tables directly in the database, for example, by using pgAdmin or psql. I thought all of the Bootstrapping interfaces were deprecated and replaced with "Conify" interfaces, but I can't find any for the config.rules tables.
The stock circ duration table includes these rules:
|1||7_days_0_renew||7 days||7 days||7 days||0|
|2||28_days_2_renew||28 days||28 days||28 days||2|
|3||3_months_0_renew||3 mons||3 mons||3 mons||0|
|4||3_days_1_renew||3 days||3 days||3 days||1|
|5||2_months_2_renew||2 mons||2 mons||2 mons||2|
|6||35_days_1_renew||35 days||35 days||35 days||1|
|7||7_days_2_renew||7 days||7 days||7 days||2|
|9||28_days_0_renew||28 days||28 days||28 days||0|
|10||14_days_2_renew||14 days||14 days||14 days||2|
|11||default||21 days||14 days||7 days||2|
The stock circ scripts (and in-db circ matrix) will always target the "default" rule here. An item circulating under this rule will start with 2 allowed renewals, and either circulate for 7, 14, or 21 days depending on the value of the item's Loan Duration field (which can have the values Short, Normal, or Long, corresponding with the shrt, normal, and extended columns in the rule table).
The circ scripts reference these rules by the value in the name column. The circ matrix tables reference these rules by the value in the id column. A common practice is to embed the values for a rule into the rule name itself, as seen above, to make it easier to understand and manage the circ scripts. It could also make sense to use names like "audiobook" or "bestseller", but those sort of labels are more often used with item circulation modifiers, to push configurability more toward end-user staff and away from admins. It also helps facilitate the configuration of rules that may be different per library in a shared system. Consider that two libraries may both have an "audiobook" circ modifier, yet based on the circ scripts, a different loan duration rule may be chosen for each of them. If the loan duration rules are named after their values, then they'll never be changed and potentially surprise a library that targets them. However, if a shared system is strong on shared policies, it may be easier to manipulate the rule table itself whenever that policy changes. It's up to you find the right balance for your system.
Need more here + examples
These files are found in /openils/var on your Evergreen server.
Someone else can tackle this one.