agglomerates that are free of gas and have lifetimes on the order of 100 Myr. It is very important to make the distinction from the start because there is often some confusion about this in the literature. In the definition used throughout this work (see Section \[sec:cluster-definition\]), ECs are *not* necessarily the direct progenitors of bound OCs, but just the natural outcome of the star formation process, which is “clustered” with respect to the field stars.

The dynamical evolution of an EC is quite complex and can progress in several possible ways, depending on both the characteristics of the recently born stellar population and the physical properties of the parent molecular cloud. A gravitationally unbound molecular cloud or an unbound region of a molecular complex might still be able to form stars in subregions that are locally bound [e.g., @Bonnell2011], but the resulting EC born there is globally unbound and quickly disperses into the field. On the other hand, within a molecular complex, especially in bound regions, many ECs might merge and form a few large entities [@Maschberger2010]. If a certain EC (once born or after merging) manages to remain gravitationally bound in the gas potential, at some point the 