2.1.1118 Part 1 Section 220.127.116.11, ph (Placeholder Shape)
a. The standard states that the placeholder idx attribute specifies the placeholder index.
The following additional restrictions apply to values on the idx attribute:
For a placeholder on a Master, Notes Master, Handout Master, Slide Layout or Notes Slide the value shall not be equal to 0xffffffff.
For any two placeholders on a Master, Notes Master, Handout Master, Slide Layout or Notes Slide the values must not be the same.
For any two placeholders on a Slide with values not equal to 0xffffffff the values shall not be the same.
For a placeholder on a Slide with a value not equal to 0xffffffff there shall be a placeholder on the Slide Layout with the same attribute values.
b. The standard does not specify the inheritance model of a placeholder shape.
PowerPoint defines a placeholder shape on a slide to inherit from the slide layout placeholder with the same idx value, and a placeholder shape on a notes slide to inherit from the notes master placeholder with the same type value.