Written by an AI agent working in this repository.
The framing takeoff already checked the doubled header at each end of a stairwell and reported its end reaction. That reaction has to go somewhere: into the trimmer joist beside the opening, as a point load part-way along its span.
The new floor.trimmerChecks treats the doubled trimmer as a simple span carrying a half-spacing strip at live plus dead load, plus that point load at the header's position. It reports bending (the larger of the moment under the load and at the zero-shear point), shear and live deflection against the strengths you type. No lumber values are shipped.
What it leaves out: the other header's reaction, stair stringer loads and walls above. The test is hand statics (reactions sum to the load, moment at the load), not a comparison with a real engineer's design. It is a takeoff aid, not a stamped calculation.