Start documenting pointers.

docs/contents/pointers.rst

@@ -0,0 +1,25 @@
+NMODL "pointers"
+================
+
+Mechanisms can refer to values in other mechanisms, e.g. the sodium current
+``ina``. Therefore, it supports a notion of "pointer", called `Datum`. A datum
+can store a pointer to a double, a stable pointer to a double, integers, or
+pointers to anything else.
+
+Integer Variables
+-----------------
+One important subset of Datum are what could be referred to as genuine pointers
+to other doubles. More precisely, pointers to parameters in other mechanisms or
+pointers to the parameters associated with each node, e.g. the voltage.
+
+These make up the majority of usecases for Datum; and are considered the
+well-mannered subset.
+
+In CoreNEURON this subset of Datums are treated differently. Because CoreNEURON
+stores the values these Datums can point to in a single contiguous array of
+doubles, the "pointers" can be expressed as indices into this array.
+
+Therefore, this subset of Datums is referred to as "integer variables".
+
+
+

docs/index.rst

@@ -19,6 +19,7 @@ About NMODL
    :caption: Contents:
 
    contents/visitors
+   contents/pointers
 
 .. toctree::
    :maxdepth: 3