Explain the limitations of view and pure

docs/contracts.rst

@@ -469,6 +469,17 @@ View Functions
 
 Functions can be declared ``view`` in which case they promise not to modify the state.
 
+The following statements are considered modifying the state:
+
+#. Writing to state variables.
+#. :ref:`Emitting events. <events>`.
+#. :ref:`Creating other contracts <creating-contracts>`.
+#. Using ``selfdestruct``.
+#. Sending Ether via calls.
+#. Calling any function not marked ``view`` or ``pure``.
+#. Using low-level calls.
+#. Using inline assembly that contains certain opcodes.
+
 ::
 
     pragma solidity ^0.4.16;
@@ -496,6 +507,13 @@ Pure Functions
 
 Functions can be declared ``pure`` in which case they promise not to read from or modify the state.
 
+In addition to the list of state modifying statements explained above, the following are considered reading from the state:
+#. Reading from state variables.
+#. Accessing ``this.balance`` or ``<address>.balance``.
+#. Accessing any of the members of ``block``, ``tx``, ``msg`` (with the exception of ``msg.sig`` and ``msg.data``).
+#. Calling any function not marked ``pure``.
+#. Using inline assembly that contains certain opcodes.
+
 ::
 
     pragma solidity ^0.4.16;