Scope of variables when using call

The proc does not inherit the variables from the caller. It will inherit all static variables and functions eg HTTP::path, but there are two ways to allow these variables in the procedure - either send them as calling variables, or use upvar.

Sending them as variables is more dependable - you don't need to worry about naming or suchlike but you can end up sending a lot of information. Add this to the procedure eg

proc process_URL {var1 var2 var3 {optionalvar "default value"} } {
...
}

You can also only have a single variable but make it a list.

Upvar depends on naming of variables to import a specific variable into the proc scope. Very useful if you want to modify the original variable, but open to errors if the variable doesn't exist or suchlike

https://www.tcl.tk/man/tcl/TclCmd/upvar.html