Rewrite GEDF_NP description.

Author: petervdonovan

packages/documentation/copy/en/reference/Target Language Details.md

@@ -2683,7 +2683,7 @@ Because the C runtime scheduler operates at a higher level of abstraction than t
 
 The following schedulers are available:
 
-- `GEDF_NP` (global earliest-deadline-first): This scheduler is the default scheduler for programs that have deadlines. It guarantees that in the execution of any given tag, reactions with earlier deadlines are executed before reactions with later deadlines; however, the tag of a reaction will still take precedence over its deadline in determining execution order. Reactions with no explicit deadline implicitly have an infinitely late deadline.
+- `GEDF_NP` (global earliest-deadline-first): This scheduler is the default scheduler for programs that have deadlines. It assigns _levels_ to reactions. The level of a reaction _r_ is the length of the longest chain of causally dependent reactions that are upstream of _r_. The `GEDF_NP` scheduler guarantees that for any pair of reactions _r_ and _s_ that have the same level and are triggered at the same tag, if the deadline of _r_ is earlier than the deadline of _s_, the execution of _r_ will never begin later than the execution of _s_. Reactions with no explicit deadline implicitly have an infinitely late deadline.
 - `NP` (non-preemptive): This scheduler is the default scheduler for programs that have no deadlines. It makes minimal guarantees about its behavior, and this allows it to include optimizations that can result in lower execution times than the GEDF_NP scheduler.
 - `adaptive`: This scheduler behaves similarly to the `NP` scheduler, with the additional limitation that it is designed for applications that can tolerate potentially wide variability in physical execution times. It performs experiments and measures execution times at runtime to determine the degree of exploitable parallelism in various parts of the program. This lets it automate judgments which are made more naively by the other schedulers and which are typically made by the programmer in general-purpose languages.
 - `GEDF_NP_CI` (global earliest-deadline-first, with chain ID): This scheduler implements the same policy as `GEDF_NP`, but it is designed for an optimization called chain ID that is described on page 92 [here](https://www2.eecs.berkeley.edu/Pubs/TechRpts/2020/EECS-2020-235.pdf). This optimization is currently disabled because it is not yet fully developed, so we advise against the use of this scheduler in practical applications.