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+# About this document
+
+This is a Work in Progress.
+
+This document describes a format for storing Static Prediction Tables.
+
+It is possible that some of all of this format will be usable as part of
+individual compressed source files, to be determined.
+
+# About Static Prediction Tables (SPT)
+
+A Static Prediction Table is a form of external dictionary, shipped either
+with the JavaScript VM, or separately, and which may be referenced by any
+number of compressed Binary AST Source Files.
+
+Shipping Static Prediction Tables makes it possible to considerably reduce
+the size of individual compressed files.
+
+This document does not attempt to document how and when a SPT is loaded,
+or how and when an individual compressed file references a SPT.
+
+# Design guidelines
+
+- A SPT must be usable by many compressed source files.
+- A VM must be able to manage several SPTs simultaneously.
+- As JavaScript is a changing language, a SPT that is complete at a given point in time may not be expected to remain
+  complete forever.
+- As Binary AST never reuses the same interface name for distinct purposes, a Path in the AST that is valid at a point
+  in time will remain valid forever.
+- For upgrade purposes, a SPT may be defined as an amendment to another SPT.
+- A SPT may define additional strings of various natures.
+
+# Format
+
+## Header
+
+The header:
+- specifies the kind of file;
+- references the grammar version;
+- optionally, references a SPT file it amends.
+
+TBD
+
+## Tables of Strings
+
+These tables add new strings that may be referenced both in the tables of probabilities
+and in the compressed files.
+
+### Table of property keys
+TBD
+
+### Table of string enum constants
+
+This table adds string enum constants. It is used when updating the JavaScript grammar.
+
+TBD
+
+### Table of interface names
+
+This table adds interface names. It is used when updating the JavaScript grammar.
+
+TBD
+
+### Table of literal strings
+TBD
+
+### Table of identifier names
+TBD
+
+
+## Tables of Probabilities
+
+These tables increase or reset to 0 the number of instances of (value) at (path).
+
+Entries with depth N look like:
+- list of
+  - the Path itself, as a list of exactly N entries of
+    - InterfaceName (as a number, exact format to be determined)
+    - Field index
+  - the distribution at this Path, as a list of
+    - Field index
+    - Value (format to be determined)
+    - Number of instances, where
+      - 0 means that we remove this (Path, Field, Value) from the probability table
+      - otherwise, if (Path, Field, Value) was in the probability table, we increase its previous number of instances
+      - otherwise, we add (Path, Field, Value) to the probability table with `Number of instances` instances.
+
+The table of probabilities contains
+- One entry of depth 0, with a single field: the root.
+- Entries of depth 1, for possible children of the root.
+- Entries of depth 2, for possible grandchildren of the root.
+- ...
+- Entries of depth D, for all other nodes.
+
+
+TBD