In the same way you have 'loop locators' it would be nice to be able to define a anacrusis/upbeat sequence with locators inside clips.In music, it is the note or sequence of notes which precedes the first downbeat in a bar. In the latter sense an anacrusis is often called a pickup, pickup note, or pickup measure, referring to the syncopation.
Imagine a melody that starts in the end of section A and continues through section B, you are limited to do this type of composition, specially in in 'session view'.
For example when you start a clip in the end of a section A, Live would play first the anacrusis/upbeat defined by locators (still inside section A) and then would loop what is defined inside 'loop locators' (inside section B).
This should be able to give you a clear idea: