Python: bit more local flow and fix ql docs

python/ql/src/semmle/code/python/dataflow/internal/DataFlowPrivate.qll

@@ -76,7 +76,6 @@ class DataFlowExpr = Expr;
  * excludes SSA flow through instance fields.
  */
 predicate simpleLocalFlowStep(Node nodeFrom, Node nodeTo) {
-
   exists(EssaEdgeRefinement r |
     nodeTo.asEssaNode() = r.getVariable() and
     nodeFrom.asEssaNode() = r.getInput()
@@ -86,6 +85,16 @@ predicate simpleLocalFlowStep(Node nodeFrom, Node nodeTo) {
     nodeTo.asEssaNode() = r.getVariable() and
     nodeFrom.asEssaNode() = r.getInput()
   )
+  or
+  exists(PhiFunction p |
+    nodeTo.asEssaNode() = p.getVariable() and
+    nodeFrom.asEssaNode() = p.getShortCircuitInput()
+  )
+  or
+  exists(EssaNodeDefinition d |
+    nodeTo.asEssaNode() = d.getVariable() and
+    nodeFrom.asEssaNode().getDefinition().getLocation() = d.(AssignmentDefinition).getValue().getLocation() // TODO: A better way to tie these together
+  )
 }
 
 //--------

python/ql/src/semmle/code/python/dataflow/internal/DataFlowPublic.qll

@@ -5,7 +5,13 @@
 import python
 private import DataFlowPrivate
 
+/**
+ * IPA type for dta flow nodes.
+ */
 newtype TNode =
+  /**
+   * A node corresponding to local flow as computed via SSA.
+   */
   TEssaNode(EssaVariable var)
 
 /**
@@ -14,8 +20,14 @@ newtype TNode =
  */
 class Node extends TNode {
 
+  /**
+   * Get the underlying SSA variable if this is such a node.
+   */
   EssaVariable asEssaNode() { this = TEssaNode(result) }
 
+  /**
+   * Get a string representation of this data flow node.
+   */
   string toString() { result = this.asEssaNode().toString() }
 
   /** Gets the enclosing callable of this node. */