  This paper is studying the critical regime of the planar random-cluster model
on $\mathbb Z^2$ with cluster-weight $q\in[1,4)$. More precisely, we prove
crossing estimates in quads which are uniform in their boundary conditions and
depend only on their extremal lengths. They imply in particular that any
fractal boundary is touched by macroscopic clusters, uniformly in its roughness
or the configuration on said boundary. Additionally, they imply that any
sub-sequential scaling limit of the collection of interfaces between primal and
dual clusters is made of loops that are non-simple.
  We also obtain a number of properties of so-called arm-events: three
universal critical exponents (two arms in the half-plane, three arms in the
half-plane and five arms in the bulk), quasi-multiplicativity and
well-separation properties (even when arms are not alternating between primal
and dual), and the fact that the four-arm exponent is strictly smaller than 2.
These results were previously known only for Bernoulli percolation ($q = 1$)
and the FK-Ising model ($q = 2$).
  Finally, we prove new bounds on the one, two and four arms exponents for
$q\in[1,2]$. These improve the previously known bounds, even for Bernoulli
percolation.
