Removing leading and trailing spaces in array elements

Shell : bash on Oracle Linux 8.6

I have a script which accepts input values as comma separated values.
My script will then read & store these values in an array and use it for various purposes.
One of my important requirement is to remove leading and trailing spaces in array elements.
So, at the script prompt, even if somebody badly enters comma separated values with leading and trailing spaces like below, it should be removed.

: John, Kate,stEwart ,Keith

From the below thread, I found a solution provided by MadeinGermany (MIG). From the last post by MIG in this thread (17-June-2023)

The below script by MIG works fine for me.
But, I don't understand what Line 23 in script is for. The one with the comment "# Substitute remaining space by dash".
I didn't quite get what 'remaining space' which MIG meant. Any idea what it is for ?

$ cat testy.sh
#!/bin/bash

CUST_DIR=/some/long/path/Linux

printf "Enter the alpha-numeric Employee ID.\nIf there are multiple Employees to process, separate the IDs using commas : "

## read -a makes it an array
IFS="," read -a employee_list

## Convert assigned values to uppercase
typeset -u emp

## Looping over array values (simpler than looping over the indexes)
for emp in "${employee_list[@]}"
do
  # In case the typeset -u does not work:
  # emp=${emp^^}
  # Delete a leading space
  emp=${emp# }
  # Delete a trailing space
  emp=${emp% }
  # Substitute remaining space by dash
  emp=${emp// /-}  ### Line 23
  echo "@$CUST_DIR/${emp}/june/process_junePayment_${emp}.sql"
done
$
$ ### Executing the script and providing the following comma separated values
$
$ ./testy.sh
Enter the alpha-numeric Employee ID.
If there are multiple Employees to process, separate the IDs using commas : John, Kate,stEwart ,Keith
@/some/long/path/Linux/JOHN/june/process_junePayment_JOHN.sql
@/some/long/path/Linux/KATE/june/process_junePayment_KATE.sql
@/some/long/path/Linux/STEWART/june/process_junePayment_STEWART.sql
@/some/long/path/Linux/KEITH/june/process_junePayment_KEITH.sql
$

Why not run the script (line by line if need be) and examine results etc ( ie debug ) , and then ask questions if still confused

Debug line by line will help only with the right input data. Otherwise (by using the provided names) the meaning of ''Substitute remaining space by dash" will remain a mystery. Try with the name " Joe Biden " to see what are the remaining spaces behind the leading and trailing one.

@resistance

see the original post as to why it's there, whether or not you need it is dependent upon input - as alluded to by @AGG2020 .