Comment # 50 on bug 1187332 from Michael Schröder

"Suggests: udev" is a very weak version of "Requires: udev". I.e. it would mean
that udev is installed *before* systemd.

Maybe you confused it with "Enhances: udev".

We have:

Requires       - normal dependency
Recommends     - weak dependency, solver tries to fulfill it
Suggests       - very weak dependencies, solver just uses it for ordering and
choosing the best package to fulfill a dependency

Supplements    - reverse variant of Recommends, the package is automatically
selected if the dependency is fulfilled
Enhances       - reverse variant of Suggests, only used for choosing the best
package