diff --git a/intl/uconv/public/nsIUnicodeEncoder.h b/intl/uconv/public/nsIUnicodeEncoder.h
index 3ce49a6532e0..e374fd1988df 100644
--- a/intl/uconv/public/nsIUnicodeEncoder.h
+++ b/intl/uconv/public/nsIUnicodeEncoder.h
@@ -20,6 +20,7 @@
 #ifndef nsIUnicodeEncoder_h___
 #define nsIUnicodeEncoder_h___
 
+#include "nscore.h"
 #include "nsISupports.h"
 
 // Interface ID for our Unicode Encoder interface
@@ -30,12 +31,79 @@ NS_DECLARE_ID(kIUnicodeEncoderIID,
 /**
  * Interface for a Converter from Unicode into a Charset.
  *
+ * XXX Think, write and doc the error handling.
+ * XXX Write error value macros
+ *
  * @created         23/Nov/1998
  * @author  Catalin Rotaru [CATA]
  */
 class nsIUnicodeEncoder : public nsISupports
 {
 public:
+
+  /**
+   * Converts the data from Unicode to a Charset.
+   *
+   * About the byte ordering:
+   * - The input stream is Unicode, having the byte order which is internal
+   * for the machine on which the converter is running on.
+   * - For output, if the converter cares (that depends of the charset, for 
+   * example a singlebyte will ignore the byte ordering) it should assume 
+   * network order. If necessary and requested, we can add a method 
+   * SetOutputByteOrder() so that the reverse order can be used, too. That 
+   * method would have as default the assumed network order.
+   *
+   * Unless there is not enough output space, this method must consume all the
+   * available input data! We don't have partial input for the Unicode charset.
+   *
+   * @param aSrc        [IN] the source data buffer
+   * @param aSrcOffset  [IN] the offset in the source data buffer
+   * @param aSrcLength  [IN/OUT] the length of source data buffer; after
+   *                    conversion will contain the number of Unicode 
+   *                    characters read
+   * @param aDest       [OUT] the destination data buffer
+   * @param aDestOffset [IN] the offset in the destination data buffer
+   * @param aDestLength [IN/OUT] the length of the destination data buffer;
+   *                    after conversion will contain the number of bytes
+   *                    written
+   * @return            XXX doc me
+   */
+  NS_IMETHOD Convert(const PRUnichar * aSrc, PRInt32 aSrcOffset, 
+      PRInt32 * aSrcLength, char * aDest, PRInt32 aDestOffset, 
+      PRInt32 * aDestLength) = 0;
+
+  /**
+   * Finishes the conversion. The converter has the possibility to write some 
+   * extra data and flush its final state.
+   *
+   * @param aDest       [OUT] the destination data buffer
+   * @param aDestOffset [IN] the offset in the destination data buffer
+   * @param aDestLength [IN/OUT] the length of destination data buffer; after
+   *                    conversion it will contain the number of bytes written
+   * @return            XXX doc me
+   */
+  NS_IMETHOD Finish(char * aDest, PRInt32 aDestOffset, PRInt32 * aDestLength)
+      = 0;
+
+  /**
+   * Returns a quick estimation of the size of the buffer needed to hold the
+   * converted data. Remember: this is an estimation and not necessarily 
+   * correct. Its purpose is to help the caller allocate the destination 
+   * buffer.
+   *
+   * @param aSrc        [IN] the source data buffer
+   * @param aSrcOffset  [IN] the offset in the source data buffer
+   * @param aSrcLength  [IN] the length of source data buffer
+   * @param aDestLength [OUT] the needed size of the destination buffer
+   * @return            XXX doc me
+   */
+  NS_IMETHOD Length(const PRUnichar * aSrc, PRInt32 aSrcOffset, 
+      PRInt32 aSrcLength, PRInt32 * aDestLength) = 0;
+  /**
+   * Resets the charset converter so it may be recycled for a completely 
+   * different and urelated buffer of data.
+   */
+  NS_IMETHOD Reset() = 0;
 };
 
 #endif /* nsIUnicodeEncoder_h___ */