diff -r cf19b7820ff0 -r 94360453bce4 docs/Writerside/topics/string.h.md
--- a/docs/Writerside/topics/string.h.md	Thu Dec 25 12:07:37 2025 +0100
+++ b/docs/Writerside/topics/string.h.md	Sun Dec 28 14:10:14 2025 +0100
@@ -49,6 +49,7 @@
 void cx_strfree_a(const CxAllocator *alloc, cxmutstr *str);
 
 
+#define CX_NULLSTR   cx_mutstr(NULL)
 #define CX_SFMT(s)   (int) (s).length, (s).ptr
 #define CX_PRIstr    ".*s"
 #define cx_strcast(s)  // converts any string to cxstring
@@ -119,23 +120,26 @@
 ```C
 #include <cx/string.h>
 
-int cx_strcat(cxmutstr *str, size_t count, ... );
+cxmutstr cx_strcat(cxmutstr str, size_t count, ... );
 
-int cx_strcat_a(const CxAllocator *allocator,
-        cxmutstr *str, size_t count, ... );
+cxmutstr cx_strcat_a(const CxAllocator *allocator,
+        cxmutstr str, size_t count, ... );
 
 size_t cx_strlen(size_t count, ...);
 ```
 
 The `cx_strcat_a()` function takes `count` UCX strings (`cxstring` or `cxmutstr` - not pointers!),
-allocates memory in `str` for a concatenation of those strings _with a single allocation_,
+reallocates the memory in `str` for a concatenation of those strings _with a single allocation_,
 and appends the contents of the strings to `str`.
 `cx_strcat()` is equivalent, except that it uses the [default allocator](allocator.h.md#default-allocator).
 
+When there is no `str` where the other strings shall be appended to, you can pass `CX_NULLSTR` as first argument.
+In that case, a completely new string is allocated.
+
 Example usage:
 ```C
-cxmutstr str = {0};
-cx_strcat(&str, 2, cx_str("Hello, "), cx_str("World!"));
+cxmutstr str = cx_strcat(CX_NULLSTR, 2,
+                         cx_str("Hello, "), cx_str("World!"));
 ```
 
 The function `cx_strlen()` sums the length of the specified strings.