Why does a displayblock affect the arguments used for accessing the
children of the nodes?

The following code creates a TreePresentation from the current working Directory:

    browser := GLMTabulator new.
    browser
        column: #tree;
        column: #text.
    browser transmit
        to: #tree;
        andShow: [ :a |
                    a tree
                        title: 'FS';
                        "display: [ :item | item basename ];"
                        children: [ :item |
                                    item isDirectory
                                        ifFalse: [ #() ]
                                        ifTrue: [ item children ] ] ].
    browser openOn: FileSystem disk workingDirectory.

As I don't want to see the FileReference printString, but the

name of the File, the first thing I tried is a displayblock like

the commented line above.

But after this change the children block does not work anymore.

The item it calls #isDirectory on, is not the FileSystem entry but the

name returned by the display block.

#format: instead of #display: works:

    browser := GLMTabulator new.
    browser
        column: #tree;
        column: #text.
    browser transmit
        to: #tree;
        andShow: [ :a |
                    a tree
                        title: 'FS';
                        format: [ :item | item basename ];
                        children: [ :item |
                                    item isDirectory
                                        ifFalse: [ #() ]
                                        ifTrue: [ item children ] ] ].
    browser openOn: FileSystem disk workingDirectory

May examples from GLMBasicExamples are using #display: , thats why

I tried this first. What is the intention to use
the display block for accessing the children?

nicolai