[exim] Need explanation for an ACL

Will anyone please explain to me what exactly the below ACL does,
specifically, where the call the spamassassin (which the site I got this
from claims is there) is made?

acl_check_content:
# Reject messages that have serious MIME errors.
# This calls the demime condition again, but it
# will return cached results.
deny message = Serious MIME defect detected ($demime_reason)
demime = *
condition = ${if >{$demime_errorlevel}{2}{1}{0}}

# Reject virus infected messages.
deny message = This message contains malware ($malware_name)
malware = *

# Always add X-Spam-Score and X-Spam-Report headers, using SA system-wide settings
# (user "nobody"), no matter if over threshold or not.
warn message = X-Spam-Score: $spam_score ($spam_bar)
spam = nobody:true
warn message = X-Spam-Report: $spam_report
spam = nobody:true

# Add X-Spam-Flag if spam is over system-wide threshold
warn message = Subject: [*SPAM*] $h_Subject
spam = nobody

# Reject spam messages with score over 10, using an extra condition.
deny message = This message scored $spam_score points. Congratulations!
spam = nobody:true
condition = ${if >{$spam_score_int}{100}{1}{0}}

# finally accept all the rest
accept