2.1.1187 Part 4 Section 4.6.23, charRg (Character Range)
For additional notes that apply to this portion of the standard, please see the notes for pRg, §4.6.56(b) .
a. The standard places no restrictions on the values of the st and end attributes.
PowerPoint requires the end attribute to be greater than the value of the st attribute and less than or equal to the length of the animated text.