diff -r 0ffb71f15426 -r 9af21a50b516 docs/src/modules.md
--- a/docs/src/modules.md	Wed May 16 19:01:21 2018 +0200
+++ b/docs/src/modules.md	Wed May 16 19:27:45 2018 +0200
@@ -589,6 +589,25 @@
 cases. If you know what you are doing, it can save you some performance,
 because you do not need the `strlen()` call.
 
+### Handling immutable strings
+
+*(Since: UCX 2.0)*
+
+For immutable strings (i.e. `const char*` strings), UCX provides the `scstr_t`
+type, which works exactly as the `sstr_t` type but with a pointer
+to `const char`. All UCX string functions come in two flavors: one that enforces
+the `scstr_t` type, and another that usually accepts both types and performs
+a conversion automatically, if necessary.
+
+There are some exceptions to this rule, as the return type may depend on the
+argument type.
+E.g. the `sstrchr()` function returns a substring starting at
+the first occurrence of the specified character.
+Since this substring points to the memory of the argument string, it does not
+accept `scstr_t` as input argument, because the return type would break the
+constness.
+
+
 ### Finding the position of a substring
 
 The `sstrstr()` function gives you a new `sstr_t` object starting with the