FitNesse treats "y" or "yes" (case insensitive) as true and "n" or "no" as false for bools.
This works with fields...
| fitlibrary.spec.SpecifyFixture | 
| 
| bool fixture |  | field | field? | field? | field? | field? | field? | field? | field? | field? | field? | field? | field? | field? |  | true | true | True | Y | y | Yes | yes | false | False | N | n | No | no |  | false | false | False | N | n | No | no | true | True | Y | y | Yes | yes |  | 
| bool fixture |  | field | field? | field? | field? | field? | field? | field? | field? | field? | field? | field? | field? | field? |  | true | true | True | Y | y | Yes | yes | false expected True actual
 | False expected True actual
 | N expected True actual
 | n expected True actual
 | No expected True actual
 | no expected True actual
 |  | false | false | False | N | n | No | no | true expected False actual
 | True expected False actual
 | Y expected False actual
 | y expected False actual
 | Yes expected False actual
 | yes expected False actual
 |  | 
...properties...
| fitlibrary.spec.SpecifyFixture | 
| 
| bool fixture |  | property | property? | property? | property? | property? | property? | property? | property? | property? | property? | property? | property? | property? |  | true | true | True | Y | y | Yes | yes | false | False | N | n | No | no |  | false | false | False | N | n | No | no | true | True | Y | y | Yes | yes |  | 
| bool fixture |  | property | property? | property? | property? | property? | property? | property? | property? | property? | property? | property? | property? | property? |  | true | true | True | Y | y | Yes | yes | false expected True actual
 | False expected True actual
 | N expected True actual
 | n expected True actual
 | No expected True actual
 | no expected True actual
 |  | false | false | False | N | n | No | no | true expected False actual
 | True expected False actual
 | Y expected False actual
 | y expected False actual
 | Yes expected False actual
 | yes expected False actual
 |  | 
..and methods...
| fitlibrary.spec.SpecifyFixture | 
| 
| bool fixture |  | set | get? | get? | get? | get? | get? | get? | get? | get? | get? | get? | get? | get? |  | true | true | True | Y | y | Yes | yes | false | False | N | n | No | no |  | false | false | False | N | n | No | no | true | True | Y | y | Yes | yes |  | 
| bool fixture |  | set | get? | get? | get? | get? | get? | get? | get? | get? | get? | get? | get? | get? |  | true | true | True | Y | y | Yes | yes | false expected True actual
 | False expected True actual
 | N expected True actual
 | n expected True actual
 | No expected True actual
 | no expected True actual
 |  | false | false | False | N | n | No | no | true expected False actual
 | True expected False actual
 | Y expected False actual
 | y expected False actual
 | Yes expected False actual
 | yes expected False actual
 |  |