displays the content if all conditions are true

SYNTAX 1 (condition as option):
{upfilter | datemax=20171225} content if true {====} content if false {/up filter}
The content if false is optional. It must be after the content if true and separated by {===} (at least 3 equal signs)

SYNTAX 2 (condition as main argument):
{up filter=datemax:20171225} content if true {====} content if false {/up filter}

SYNTAX 3 (mono-shortcode):
{upfilter | guest=0 | return-true=REGISTER | return-false=GUEST}
--> guest=0 is true if a user is logged in
--> the returned value is entered as an option

SYNTAX 4 (multi-conditions):
{upfilter=day:2,3; hperiod:0900-1200,1500-1900 | return-true=OPEN | return-false=CLOSED}
--> true if Monday or Tuesday between 9am-12pm or 3-7pm