Clarification Request: Table.ToNavigationTable's itemNameColumn Param

[bgribaudo]

Perhaps https://github.com/MicrosoftDocs/powerquery-docs/issues/287 would better be answered over in this project. However, unfortunately, I don't have access to a move issue button, so reposting that issue's text below here.

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Under section "Table.ToNavigationTable", that function's itemNameColumn is described as follows:

The name of the column to use to determine the preview behavior. This is typically set to the same value as itemKind.

Could you clarify the specifics of what values are expected to be found in the column that's referenced, and how those values will be interpreted? (Example: If I specify the itemNameColumn as "Col1" from my nav table, what values in that column will Power Query interpret as telling it to delay vs. not to delay previewing).

Per https://github.com/microsoft/DataConnectors/issues/30, it sounds like a good way to test the preview behavior is to add a function to the navigation table. If the nav table display shows input boxes for the function's params, the function had its preview delayed; if no param input controls are displayed, preview was not delayed.

Using the test code below, it appears that previewing is not delayed if this param set to a text value, regardless of whether that value is a column name in the nav table, and previewing is delayed if the param is set to null, a logical or a number.

Clarification on how this param works would be most appreciated! -) Thanks!

Example Tester:

[DataSource.Kind="MyTester", Publish="MyTester.Publish"]
shared MyTester.Contents = () =>  
    let
        SomeFunction = (a as text) => Text.Upper(a),
        Base = 
            #table({"Name", "Data", "ItemKind", "ItemName", "IsLeaf"}, 
            {
                {"string: 'Function' [literal value typically found in ItemType column] (Params Don't Preview)", SomeFunction, "Function", "Function", true},
                {"string: 'Non-Existent Column' [invalid column name] (Params Don't Preview)", SomeFunction, "Function", "Non-Existent Column", true},
                {"string: 'Name' [valid column name] (Params Don't Preview)", SomeFunction, "Function", "Name", true},
                {"string: 'Data' [valid column name] (Params Don't Preview)", SomeFunction, "Function", "Data", true},
                {"Null (Params Preview)", SomeFunction, "Function", null, true},
                {"false (Params Preview)", SomeFunction, "Function", false, true},
                {"true (Params Preview)", SomeFunction, "Function", true, true},
                {"123 (Params Preview)", SomeFunction, "Function", 123, true}
            }
        )
    in
        Table.ToNavigationTable(Base, {"Name"}, "Name", "Data", "ItemKind", "ItemName", "IsLeaf");

---

Notes after further testing:

It looks like Table.ToNavigationTable's param itemNameColumn (which maps to metadata field Preview.DelayColumn on the navigation table that's returned) has the following effects:

• If, for a given row, the column corresponding to itemNameColumn contains a text value:
  • That value will be used as the text displayed in the navigation table's Data column.
    Example: see red marks, below.
    
  • The Data column's value will have its previewing delayed.
• If, for a given row, the column corresponding to itemNameColumn contains something other than a text value:
  • The value from the column identified by itemKind will be used as the text in the nav. table's Data column.
    Example: see blue marks, above.
  • The Data column's value will not have previewing delayed.

Can you confirm/correct the above, and if correct, clarify the docs for this param?

Thanks!