docs(iso): Explain sed in_array_remove_n mechanism (#6)

setup.sh

@@ -526,6 +526,23 @@ function in_file_in_array_remove_n () {
     arg_file="${1:?}"
     arg_array="${2:?}"
     arg_string="${3:?}"
+
+    # Look for any line that contains "${arg_string}", delete that string
+    #
+    # For following example text we're assuming that:
+    # - "${arg_array}"   equals 'HOOKS'
+    # - "${arg_string}"  equals 'fsck'
+    #
+    # First -e expression removes 'fsck' wherever it is defined as the one
+    # and only element of any HOOKS=(fsck) should such a line exist.
+    #
+    # Second -e expression finds string 'fsck' where it's preceded by space
+    # character(s) and followed by either space character(s) or a closing
+    # parenthesis.
+    #
+    # Third -e expression finds string 'fsck' where it's preceded by space
+    # character(s) or an opening parenthesis and followed space
+    # character(s).
     sed -ri \
         -e 's'$'\x1''((\()('"${arg_string}"')(\)))'$'\x1''\2\4'$'\x1''g' \
         -e 's'$'\x1''('"${arg_array}"'=.*?)([[:space:]]+'"${arg_string}"')([[:space:]]+|\))'$'\x1''\1\3'$'\x1''g' \