The problem that occurs if we remove the quotation marks is that the parameter text is no longer included in the output, we see only Text: .

To understand why, consider for a moment what the $wikify widget does: It takes the text presented to it in the text parameter and wikifies it. When we have quoted the value of text, it gets exactly the wikitext we specified, namely the text Text: and then a procedure call. The widget makes this procedure call and gets the value Text: <<text>>. It sees there is still wikitext to wikify, and does so again in the same context, where text is still defined as a variable due to being a parameter of the procedure. It gets the value of the text variable, which is test text, sees there is no remaining wikitext to wikify, and sets the variable wikitext to the result, which is Text: test text, as we want.

Now what about if we haven't quoted the value of text? Now, before the $wikify widget gets to it at all, TiddlyWiki will evaluate the value of <<myText "test text">>. When TiddlyWiki evaluates the procedure call, it gets the literal text Test: <<text>>. Because the wikitext being evaluated is the value of an attribute, TiddlyWiki does not attempt to wikify this again. Instead it stops and passes this text in to the $wikify widget. Now the $wikify widget tries to wikify this string. But the variable text is no longer defined, because the $wikify widget is a different context – it was only defined during the evaluation of the initial procedure call (which was not repeated enough times to get the value of the text variable, since it was the value of an attribute)! Since text now has no value, the $wikify widget treats it as empty and puts just Text: in the value of the wikitext variable, and we get the incorrect result.

This quirk is not specific to procedure calls – macros using <<__parameters as variables__>> have the same problem. It does not, however, happen with text substitution, since in that case the initial macro call results in immediate replacement of the placeholders with their parameters – there's nothing to wikify.