[#1] runtime errors documented

docs/compile-time-options.md

@@ -105,4 +105,4 @@ You may redefine [private and protected fields](field-types.md) prefixes with se
 ERL_COMPILER_OPTIONS='[{d, cloak_priv_prefix="hidden_"}, {d, cloak_prot_prefix, "readonly_"}]'
 ```
 
-All record fields starting with `hidden_` will be threated as private, and ones starting with `readonly` will be threated as protected.
+All record fields starting with `hidden_` will be threated as private, and ones starting with `readonly` will be threated as protected.

docs/index.md

@@ -7,4 +7,4 @@
 * [Exporters](exporters.md): different ways to export data with user-defined callbacks
 * [Substructures](substructures.md): explanation of nested data structures `cloak` supports
 * [Known issues](known-issues.md)
-* [Contributing](contributing.md)
+* [Contributing](contributing.md)

docs/runtime-errors.md

@@ -0,0 +1,13 @@
+# Runtime errors
+
+TL;DR: `cloak` will `throw` the standard `badarg` error in every case other than happy-path one.
+
+It means that you should wrap critical sections of your code with `try..catch` to avoid process crash.
+
+## Validation errors
+
+Validation errors will be generated in case of:
+
+* [Required field](field-types.md) was not found in `Module:new/1` argument map;
+* Field value [validation](validators.md) failed with any reason;
+* Any of `Module:Getter/1`, `Module:Setter/2`, `Module:update/2`, `Module:export/1` functions being called with wrong type of argument, e.g. invalid value passed instead of `Module` internal record (`Module:t()`).