Why am I not able to parse valid XML straight from the Salesforce Documentation, but JSON works fine?

Question

On this particular page: https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_rest_methods.htm

About halfway down, you'll see a method which I have included in my class

@RestResource(urlMapping='/Cases/*')
global class MyClassPostStudy{

@HttpPost
    global static void myPostMethod(String s1, Integer i1, Boolean b1, String s2){
        system.debug('this hit');
    }
}

By going to Workbench and using the REST Explorer - I'm able to parse the JSON in the example just fine.

{
  "s1" : "my first string",
  "i1" : 123,
  "s2" : "my second string",
  "b1" : false
}

However I'm getting an error when I parse the XML example:

<request>
  <s1>my first string</s1>
  <i1>123</i1>
  <s2>my second string</s2>
  <b1>false</b1>
</request>

message: Unexpected character ('<' (code 60)): expected a valid value (number, String, array, object, 'true', 'false' or 'null') at [line:1, column:2] errorCode: JSON_PARSER_ERROR

Answer 1

I figured it out - I needed to go into the 'Headers' button in Workbench and change the

Content-Type: application/JSON; charset=UTF-8 
Accept: application/JSON

to

Content-Type: application/xml; charset=UTF-8
Accept: application/xml