Q:

Specific placeholder id in pptx file

Does anybody know why this value is used p:ph idx="4294967295"?
As I see it's a specific value for MS PP which changes MS PP behavior. I've read openxml standard, but I haven't found anything information related to this number.
Part of the OOXML scheme below:
<p:sp>
        <p:nvSpPr>
          <p:cNvPr id="15364" name="Text 4" />
          <p:cNvSpPr>
            <a:spLocks noGrp="1" />
          </p:cNvSpPr>
          <p:nvPr>
            <p:ph idx="4294967295" />
          </p:nvPr>
        </p:nvSpPr> 
           ...
</p:sp>

A:

I've investigated and understood how to get this value in PP. For example, you have an inheritance chain: master slide placeholder with idx='1', slide layout placeholder with idx='1', and slide placeholder with idx='1'. if you remove the slide layout's placeholder the inheritance chain between the slide and the slide layout will be broken, but PP still has to inherit properties from parent entities in this case from the master slide, and it marks slide placeholder with idx='4294967295'. It's like a mark. If PP reads this value it inherits properties directly from the master slide, excludes the slide layout and it understands that placeholder which belongs to the slide layout has been removed.
How does it find the required placeholder if the slide placeholder changes from idx='1' to idx='4294967295'? I think MS PP does it by placeholder type, but I am not sure.
This article may be useful Placeholder on master slide

