Tryst::UI::FlowConfig
Flow-packing config for a column/row-style container - side/ main_pad/cross_pad/main_fill/cross_fill/anchor. A convenience over overriding #arrange for exactly this shape: giving flow: to WidgetType.new is enough for #arrange's own default body to delegate to Realizer#arrange_flow with this data, so most flow containers never need to touch #arrange directly. A dedicated record rather than a Hash(Symbol, TclArgValue) (unlike opts/layout elsewhere) - ruby's own flow: hash nests another hash for anchor:, which doesn't fit TclArgValue's closed union, and this is realize-internal metadata that was never going to reach App#command as a real Tk option anyway.
Constants
Top-to-bottom stacking: what ui.column is, and what every container that "just stacks its children" (panel, group, tab, pane, window) shares with it, so gap:/pad:/align: and a child's grow: mean the same thing on all of them.
Constructors
Instance methods
The Tk anchor letter for each align: this container understands. FlowAlign::Stretch is absent on purpose - it fills the cross axis instead of anchoring, so it never reaches a lookup here.