  Recent progress in understanding subcritical transition to turbulence is
based on the concept of the edge, the manifold separating the basins of
attraction of the laminar and the turbulent state. Originally developed in
numerical studies of parallel shear flows with a linearly stable base flow,
this concept is adapted here to the case of a spatially developing Blasius
boundary layer. Longer time horizons fundamentally change the nature of the
problem due to the loss of stability of the base flow due to
Tollmien--Schlichting (TS) waves. We demonstrate, using a moving box technique,
that efficient long-time tracking of edge trajectories is possible for the
parameter range relevant to bypass transition, even if the asymptotic state
itself remains out of reach. The flow along the edge trajectory features streak
switching observed for the first time in the Blasius boundary layer. At long
enough times, TS waves co-exist with the coherent structure characteristic of
edge trajectories. In this situation we suggest a reinterpretation of the edge
as a manifold dividing the state space between the two main types of boundary
layer transition, i.e. bypass transition and classical transition.
