[eureka]

Pure guess, but it works. I didn't look at its internals and don't know anything about possible additional parameters, except dialog's name.

lipc-set-prop com.lab126.pillow customDialog '{"name": "sample_custom_dialog"}'

To hide it:

lipc-set-prop com.lab126.pillow interrogatePillow '{"pillowId": "sample_custom_dialog", "function": "nativeBridge.dismissMe()"}'

(There should be another, official way to close Pillow windows from shell prompt, but it's all I can come to ATM.) I believe, I was wrong. There is no common method to close Pillow windows via LIPC (except nativeBridge.dismissMe function).

I don't know how about PW, but KT's pillow looks for HTML files, dialogs included, also at /usr/local/tests/pillow (tested on 5.3.2.1).

UPD: ha, I've just found my old notes about Pillow regarding customDialog property:

/usr/local/tests/pillow (fallback of /usr/share/webkit-1.0/pillow)

To load stock Pillow scripts from HTML placed in fallback location:
<script src="///usr/share/webkit-1.0/pillow/javascripts/sample_custom_dialog.js">

To show example.html:
lipc-set-prop com.lab126.pillow customDialog '{"name": "example"}'

To show example/index.html
lipc-set-prop com.lab126.pillow customDialog '{"name": "example/index"}'

To set parameters:
lipc-set-prop com.lab126.pillow customDialog '{"name": "sample_custom_dialog", "clientParams": {"dismiss": true}}'

sample_custom_dialog handles dismiss parameter and closes itself on receiving it.