Suppose I have input xml like following:

Element #1.
<serial-port port=3D"port1" type=3D"control" baud=3D"38400" parity=3D"none"=
/>

Element #2. //differ in @type with element #1.
<serial-port port=3D"port1" type=3D"status" baud=3D"38400" parity=3D"none"/=
>

Element #3. //same as element #2.
<serial-port port=3D"port1" type=3D"status" baud=3D"38400" parity=3D"none"/=
>

Element #4.
<serial-port port=3D"port1" type=3D"relay" baud=3D"38400" parity=3D"none"/>

Element #5.  //differ in @baud with element #2.
<serial-port port=3D"port1" type=3D"status" baud=3D"115200" parity=3D"none"=
/>

Element #6.
<serial-port port=3D"port2" type=3D"relay" baud=3D"115200" parity=3D"none"/=
>

Base on my rules at the end, I wound like to have desired output as
following. Note there are 6-input elopements and

resulting 5-output elements with Element #1 and #2 being combined into
one. How can this be done with XSLT?

<SerialPort> //Combines Element #1 and #2: rules 2.0 and 2.1
   <Port>port1</Port>
   <Type>status-control</Type> //control-status also OK, they are
to
                               //be treated the same in parsing
program.
   <Baud>38400</Baud>
   <Parity>none</Parity>
</SerialPort>

<SerialPort> //Element #3. Although it is qualified to be combined
with element #1 in the output,
             //due to the fact that Element #1 has been taken. Leave
alone per rule 2.2
   <Port>port1</Port>
   <Type>status </Type>
   <Baud>38400</Baud>
   <Parity>none</Parity>
</SerialPort>

<SerialPort> //Element 4. Leave alone per rule 2.1 - @type of 'relay'
can't be combined with others.
   <Port>port1</Port>
   <Type>relay</Type>
   <Baud>38400</Baud>
   <Parity>none</Parity>
</SerialPort>

<SerialPort> //Element 5. Leave alone per rule 2.0 - not matching
@Baud for 'port1' with @type of 'control'.
   <Port>port1</Port>
   <Type>status</Type>
   <Baud>115200</Baud>
   <Parity>none</Parity>
</SerialPort>

<SerialPort> //Element 6. Leave alone per rule 2.1 - @type of 'relay'
can't be combined with others.
             //Or rule 2.0 - there is no other <serial-port> with same
@port.
   <Port>port2</Port>
   <Type>relay</Type>
   <Baud>115200</Baud>
   <Parity>none</Parity>
</SerialPort>

Here are my rules:

1.0 @type has valid values of:  status, control, and relay.
2.0 Only <serial-port> of same @port (the key), @baud, and @parity can
be combined.  And,
2.1 The two to be combined elements must have different @type, and the
@type must be either =91status=92 or =91control=92.  And,
2.2 Each <serial-port> can be combined only once.