docs: update to define integer overflow

Change-Id: Ie8a1b31035f2d27a220e5df2e9e178ec3b39ee68

doc/manual/src/language/operators.md

@@ -67,8 +67,12 @@ After evaluating *attrset* and *attrpath*, the computational complexity is O(log
 
 ## Arithmetic
 
-Numbers are type-compatible:
-Pure integer operations will always return integers, whereas any operation involving at least one floating point number return a floating point number.
+Numbers will retain their type unless mixed with other numeric types:
+Pure integer operations will always return integers, whereas any operation involving at least one floating point number returns a floating point number.
+
+Evaluation of the following numeric operations throws an evaluation error:
+- Division by zero
+- Integer overflow, that is, any operation yielding a result outside of the representable range of [Nix language integers](./syntax.md#number-literal)
 
 See also [Comparison] and [Equality].
 

doc/manual/src/language/syntax.md

@@ -183,6 +183,13 @@ This section covers syntax and semantics of the Nix language.
   Numbers, which can be *integers* (like `123`) or *floating point*
   (like `123.43` or `.27e13`).
 
+  Integers in the Nix language are 64-bit [two's complement] signed integers, with a range of -9223372036854775808 to 9223372036854775807, inclusive.
+
+  [two's complement]: https://en.wikipedia.org/wiki/Two%27s_complement
+
+  Note that negative numeric literals are actually parsed as unary negation of positive numeric literals.
+  This means that the minimum integer `-9223372036854775808` cannot be written as-is as a literal, since the positive number `9223372036854775808` is one past the maximum range.
+
   See [arithmetic] and [comparison] operators for semantics.
 
   [arithmetic]: ./operators.md#arithmetic