Template:Params
Params is used to pass the parameters of the template called to another template. It returns a bar | separated list of the parameters. So far it will only return up to any 20.
If {{Params|{{{1}}}}|{{{2}}}}|{{{3}}}}|{{{4}}}}} is called from inside a template call
{{foo|Param_1|Param_2|Param_3|Param_4|Param_5|Param_6}},
then it will return
Param_1|Param_2|Param_3|Param_4.
Concatenating calls to Params can be used return more parameters.
{{Params|{{{2}}}}|{{{3}}}}|{{{4}}}}}|{{Params|{{{6}}}}|{{{5}}}}}
will return
Param_2|Param_3|Param_4|Param_6|Param_5