When you use the is operator, it needs a list of titles to precede it:
When you use the "all" operator, it generates its own title list just like
"tag[Mohammad]" finds all the tiddlers tagged with "Mohammad".
Certain operators, like "title", "tag", and "all" are generators -- they
generate a list of items from the entire wiki. To see this, try this at
TiddlyWiki.com:
<$list filter="01 02 03">
<$set name="xx" filter="[tag[HelloThere]all[current]addprefix[Lec]]"
emptyValue="No output">
<<xx>>
</$set>
</$list>
Even though "tag[HelloThere]" generates a half dozen tiddlers, you only
see the standard 3 outputs. This is because "all[current]" ignored it's
input and generated it's own items based on the current tiddler. However,
"tag" is extra, extra special in that it can generate tiddlers when at the
start of a list, but work as a filter when in the middle. We use tag so
often that it's easy to take this extra ability for granted.
-- Mark
On Sunday, February 3, 2019 at 11:06:27 AM UTC-8, Mohammad wrote:
>
> S.S, Mark and BTC,
> Many thanks for your kind reply. Still I am confused.
>
> See also the below description by Tobias Beer. This is also nice example.
>
>
> http://tobibeer.github.io/tw/filters/#when%20current%20tiddler%20has%20title
>
>
> Actually I think when I have
>
> <$list filter="01 02 03">
> here I have a local variable called *currentTiddler* and I can use it.
>
>
>
> but, it seems *is[current] *IS only refer to the title of tiddler, and
> differs from the currentTiddler above (a loop variable)
>
> I am trying to read and understand the documentation.
>
> --Mohammad
>
>
> On Sunday, February 3, 2019 at 8:32:27 PM UTC+3:30, S. S. wrote:
>>
>> Mohammad, the explanation by BurningTreeC is the really the key to
>> understanding the issue here.
>>
>> the *all* operator creates an output, ignores every input. the *is*
>>> operator filters an input
>>>
>>
>> I guess the first : <$list filter="01 02 03"> : is just setting the
>> <<currentTiddler>> variable. The *all* operator can use that, the *is*
>> operator ignores it?
>>
>> I believe this difference between "creating an output" and "filtering an
>> input" deserves to be clarified the documentation, and I may do that.
>>
>> Also, Mark said:
>>
>> The "is" operator has the advantage that it can take a "system"
>>> parameter, which is for some reason is missing from "all".
>>>
>>
>> As a general question, would it not be a good idea to include a
>> fundamental category of *system* in the *all* operator?
>>
>>
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