register a variable through a hook

[emath]

now i dont get an error though this if :

<vb:if condition="$diffPrev['bool']=true"> 555 </vb:if>

always gives true (even if in the last URL didnt have "pitronot" in it)

and this : {vb:raw $diffPrev.bool} gives nothing .

btw, why do i need to preRegister the variable if its a hook ?

* ofcourse im writing this codes in the search_threadbit template *