PHost maintains a list of pending build orders. This list is remembered between turns.
Each turn, PHost scans all starbases for new ship build orders. These are placed into the ship build queue. This scan starts at a random starbase, so that low-Id starbases don't have advantages: every base has the same chance to be chosen first. The new orders are generally appended to the end of the build queue, where they wait until all orders before them are processed.
After collecting build orders, PHost attempts to build new ships by looking at the head of the queue. As long as enough ship slots are free, the whole queue can be processed immediately, so that build orders are performed in the same turn they were submitted in, during the ship building phase. As soon as all ship slots are used up, build orders start to accumulate in the queue.
The build queue mode (BuildQueue) decides in which order to perform the builds. Therefore, each build order is associated with a priority. The highest-priority order is performed first.
Players can affect these priorities using their build points (Player Activity Level, PAL). Build points are awarded for risky game actions: the more active you play, the faster you can build. The build points collected in one turn are called Turn Activity Level (TAL).
Normally, the order in which your ships are built is the order in which you submit your build orders. You can designate some build orders as Priority Builds to have them performed earlier than the others.
To use Priority Builds, the AllowPriorityBuild config option must be enabled. You can then use the PBn friendly codes to affect the order of build.
Note that the PBn friendly codes are considered special by PHost and will, therefore, never match for the purposes of combat, beam-gather, etc. Note also that PB0 is not an override code and is not in any way a special friendly code.
Changing Build Orders: When you change a build order before the ship is built, the new build order normally starts walking the build queue anew, as if the previous order had never been there. PHost can be configured to allow the new order to inherit some of the old order's priority using the BuildChangeRelativePenalty option. That option specifies how much priority a changed build order loses compared to the previous one, and defaults to 100% (=complete loss). At a value of 25, for example, a build order would lose only one-fourth of its priority, and therefore start in the front quarter of the queue instead of at its end.
Historically, there also is an option SBQBuildChangePenalty which specifies a fixed penalty. That option only works in PAL queue mode, see below. It specifies a penalty given in addition to BuildChangeRelativePenalty.
