FFstrbuf: clarify usage requirements for ffStrbufGetdelim and friends

src/common/FFstrbuf.h

@@ -103,6 +103,10 @@ FF_C_NODISCARD uint64_t ffStrbufToUInt(const FFstrbuf* strbuf, uint64_t defaultV
 void ffStrbufUpperCase(FFstrbuf* strbuf);
 void ffStrbufLowerCase(FFstrbuf* strbuf);
 
+// Function alters the buffer to extract lines or delimited segments (replaces the delimiter with '\0')
+// so that buffer MUST be heap allocated (NOT a static string)
+// `lineptr` must be `NULL` and `n` MUST be `0` for the first call
+// Caller MUST NOT free `*lineptr`
 bool ffStrbufGetdelim(char** lineptr, size_t* n, char delimiter, FFstrbuf* buffer);
 void ffStrbufGetdelimRestore(char** lineptr, size_t* n, char delimiter, FFstrbuf* buffer);
 
@@ -111,10 +115,14 @@ void ffStrbufGetdelimRestore(char** lineptr, size_t* n, char delimiter, FFstrbuf
  *
  * @details Behaves like getline(3) but reads from a FFstrbuf.
  *
- * @param[in,out] lineptr The pointer to a pointer that will be set to the start of the line.
- *                         Can be NULL for the first call.
+ * @param[in,out] lineptr The pointer to a pointer that will be set to the start of the line
+                          (points to buffer's internal memory address to avoid memory allocation and copy).
+                          MUST NOT be freed by the caller, unlike `getline(3)`.
+ *                        MUST be NULL for the first call.
  * @param[in,out] n The pointer to the size of the buffer of lineptr.
- * @param[in] buffer The buffer to read from. The buffer must not be a string literal.
+                    MUST be 0 for the first call.
+ * @param[in] buffer The buffer to read from.
+                     MUST be heap allocated (NOT a static string).
  *
  * @return true if a line has been read, false if the end of the buffer has been reached.
  */
@@ -124,7 +132,7 @@ static inline bool ffStrbufGetline(char** lineptr, size_t* n, FFstrbuf* buffer)
 }
 /**
  * @brief Restore the end of a line that was modified by ffStrbufGetline.
- * @warning This function should be called before breaking an ffStrbufGetline loop.
+ * @warning This function should be called before breaking an ffStrbufGetline loop if `buffer` will be used later.
  */
 static inline void ffStrbufGetlineRestore(char** lineptr, size_t* n, FFstrbuf* buffer)
 {