From Paolo Mozzati:

I tried to schedule a job that performed a daily backup through anacron on Fedora 27 on my laptop. I didn't understand why it worked by chance. I read a lot of documentation including https://docs.fedoraproject.org/f27/system-administrators-guide/monitoring-and-automation/Automating_System_Tasks.html#s1-autotasks-cron-anacron

It explains how to set up anacron and the structure of anacrontab file but not the actual process Fedora uses to run the anacron command.
I found usefull this answer:

In CentOS/RHEL, anacrontab is run from cron... so you don't need to do anything.

    1. cron.{daily, weekly, monthly} jobs are defined in /etc/anacrontab
    2. The anacron command executes jobs defined in /etc/anacrontab
    3. Anacron is called from /etc/cron.hourly/0anacron
    4. /etc/cron.d/0hourly contains 01 * * * * root run-parts /etc/cron.hourly

found at: https://serverfault.com/questions/657936/do-i-need-to-restart-after-editing-anacrontab

So i look in /etc/cron.hourly/0anacron. Here the content:

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#!/bin/sh
# Check whether 0anacron was run today already
if test -r /var/spool/anacron/cron.daily; then
    day=`cat /var/spool/anacron/cron.daily`
fi
if [ `date +%Y%m%d` = "$day" ]; then
    exit 0
fi

# Do not run jobs when on battery power
online=1
for psupply in AC ADP0 ; do
    sysfile="/sys/class/power_supply/$psupply/online"

    if [ -f $sysfile ] ; then
        if [ `cat $sysfile 2>/dev/null`x = 1x ]; then
            online=1
            break
        else
            online=0
        fi
    fi
done

It seems to me that anacron runs only when AC power is supplied. This could be a problem since anacron is meant to be used on machine that are not always on. Typically, as was for me, a laptop that is often powered by battery. This means that my backup script could never run. I do understand that is quite dangerous to run a job running the risk to have your machine shutted down.
Maybe you can indicate in the wiki that anacron run only when the machine is connected to AC.

Besided, i read in fedora guide:
"Both Cron and Anacron are daemons..."
As I understand so far anacron is not a daemon but just a command ran by crond.

I hope this could be useful for someone else.
Best regards.
Paolo Mozzati