Observations meets theory in clustered star formation
  Stars form predominantly in groups which display a broad spectrum of masses,
sizes, and other properties. Despite this diversity there exist an underlying
structure that can constrain cluster formation theories. We show how combining
observations with simulations allows to disclose this underlying structure. One
example is the mass-radius relation for young embedded associations which
follows $M_c = CR_c^\gamma$ with $\gamma$ = 1.7 $\pm$0.2, which is directly
related to the mass-radius relation of clumps. Results based on GAIA 2D have
demonstrated that young stellar groups (1--5 Myr) expand and that this
expansion process is largely over by an age of 10-20 Myr. Such a behaviour is
expected within the gas expulsion scenario. However, the effect of gas
expulsion depends strongly on a the SFE, the gas expulsion time scale, etc.
Here it is demonstrated how existing and upcoming data are able to constrain
these parameters and correspondingly the underlying models.
