expansionMemory property
Maximum number of entries in _rememberedExpansion. When exceeded,
the oldest are evicted: Dart maps iterate in first-insertion order,
and re-recording an existing key does not move it, so eviction is
FIFO by when a key was FIRST remembered. 0 disables the memory
entirely: nothing is remembered or restored across remove/re-add.
Implementation
final int expansionMemory;