We like one liner code examples, they can be tested using the unit tests if a result is given. Just omit `cfset` and semicolons, for example:
left("Peter", 4)
If you specify the result of the example, for example in this case Pete and it is a one liner like above your example will be tested automatically by the Travis CI build (you can also run the test locally /tests/run.cfm.
When you click the Run Code button, the above code example will be converted to the follow so it can run and show the output in TryCF:
<cfoutput>#left("Peter", 4)#</cfoutput>
If a code example has semicolons it is assumed to be script and would be wrapped in a cfscript tag when the Run Code button is clicked.