Created attachment 196828 [details]
custom placeholder text.pptx: created in PowerPoint 2010

A master slide can contain placeholder textboxes - which contain strings that are not seen in a slideshow, nor are printed. In MS PowerPoint this text can be customized to say whatever you want, but in LO these are uneditable, pre-defined strings (like STR_PRESOBJ_TITLE", "Click to add Title" or STR_PRESOBJ_MPTITLE", "Click to edit the title text format")

For a long time (at least since LO 5.3) LO has displayed MSO's custom text in the master page view. However, that custom placeholder text has never been displayed on the slide layout. Instead, SdPage::GetPresObjText() just uses the STR_PRESOBJ_* strings. [LO crashes in old versions when I try to look at the master slide, so I don't know when support for custom placeholder text started.]

AFAICS, while ODF allows importing/exporting these customized strings, there is no way in the UI to create or modify them.

PPTX indicates customized placeholders with:  <p:ph ... hasCustomPrompt="1"/>


Steps to reproduce:
1.) Open custom placeholder text.pptx. (Note two empty slides. The first slide has a title box with "Click to add Title" instead of "Custom Title 1")
2.) Switch to master slide view (View - Master Slide). (Note the title is "Custom Title 1" as expected).

Now to be honest, I'm not sure it is a good idea to do what this bug report is requesting. My reasoning relates to how confused the user will likely be when that customized text is NOT displayed during the slideshow. Much better is our consistent, action-oriented strings which instruct the user to fill in the desired content.