[region] README

src/plugins/region/README.md

-# Region Analysis plugin
+# Region Analysis plugin (experimental)
 
 Region is a plugin for Frama-C that implements a new memory and alias analysis.
+This is a work in progress in early design stage.
+
+## Usage
+
+Regions are computed on demand from the registered Server requests.
+
+Command line option `-region` can be used to compute regions for all functions
+and dump on output the result analysis. With `-region-debug 1+` typed accesses
+are also reported.
+
+An API will be provided soon.
+
+## Annotations
+
+Behavior annotation `\region::region` and code annotation `\region::alias`
+can be used to specify supplementary aliases and to name regions.
+The syntax is the same:
+
+```
+//@ region [A:] lv, … , lv ;
+```
+
+Such a specification put all the l-values in the same region. A name can be
+given to the region, and reused later to put other l-values on the same region.
+Several regions can be specified in a single annotation.
+
+Unnamed regions from different annotations refer to _different_ regions unless
+they are aliased by sharing common l-values.
+
+L-values in region annotations use a similar syntax to ACSL terms.
+However, array access and pointer arithmetics must be specified with unlimited range, eg. `a[..]` or `*(p+(..))`.
+
+A syntax for specifying field aliasing and input/output array shapes will be provided soon.
+
+## Current Limitations
+
+Currently, ACSL contracts are not taken into account except for region
+annotations. Function calls are totally incomplete, and aliases that would be
+produces by function calls are not _yet_ taken into account. Use `//@alias` code-annotations as a temporary work around.
+
+## Ivette Support
+
+The Region Analysis component can be used to compute and visualize regions.
+Tooltips print access types to each regions.
+
+Colored regions means the following:
+ - _Red_ regions are those accessed with incompatible types
+ - _Yellow_ regions are constant pointers
+ - _Orange_ regions are written pointers
+ - _Green_ regions are RW regions
+ - _Pink_ regions are written-only regions (might be drop)
+ - _Grey_ regions are read-only regions (constant, no memory)
+
+Regions access and localization of currently selected marker will be
+provided soon.