They're swash variants of standard characters. The reason they show up in the glyph palette as "null" is because there are no standard Unicode values for swash characters, and names are not required by the TrueType format.

So those are just swashified A and L glyphs?

I feel like a child learning how babies are made.

They are swash versions of "a" and "l" (lowercase L). If you use the font in a "Cocoa" app, such as TextEdit, open the Fonts window and select "Typography" from the little "gear" pop-up near the bottom left, you can see that there are several swash and alternate versions:

If you enable the Character Viewer (from the Keyboard preferences in the System Preferences app), you can see all the different forms available for each basic character (such as lowercase L):

But, since Apple Chancery is an AAT (Apple Advanced Typography) font, not an OpenType font, InDesign doesn't recognize any of this. AAT is an extension of TrueType that preceded OpenType. It can do similar things (like swashes and alternates), but only works on Macs. It's probably because it's not cross-platform compatible that Adobe doesn't do much to support it in InDesign and their other apps.

However, you can use the Character Viewer to insert these special characters into an InDesign document.

Well I certainly didn't even know that about text/edit, thank-you! That's useful. Interestingly though on my system that particular glyph doesn't show up as an alternate for L. It does for the A. I'll just file that under software oddities and try to forget about it though.

Thanks much for entertaining a possibly over-enthusiastic student digging around in the character palettes and such!

It's an alternate for "l" (lowercase L), not "L" (uppercase L). That may be why it's not showing up on your system.

In any case, any characters you see in InDesign's glyph palette can be inserted into your text at the cursor position by double-clicking in the glyph palette.