diff --git a/public/fpdfview.h b/public/fpdfview.h
index 1cd3d6d..6978012 100644
--- a/public/fpdfview.h
+++ b/public/fpdfview.h
@@ -112,7 +112,14 @@
 // system wide string by yourself.
 typedef const char* FPDF_STRING;
 
-// Matrix for transformation.
+// Matrix for transformation, in the form [a b c d e f], equivalent to:
+// | a  b  0 |
+// | c  d  0 |
+// | e  f  1 |
+//
+// Translation is performed with [1 0 0 1 tx ty].
+// Scaling is performed with [sx 0 0 sy 0 0].
+// See PDF Reference 1.7, 4.2.2 Common Transformations for more.
 typedef struct _FS_MATRIX_ {
   float a;
   float b;
@@ -667,9 +674,10 @@
 //                          output buffer). The bitmap handle can be created
 //                          by FPDFBitmap_Create or retrieved by
 //                          FPDFImageObj_GetBitmap.
-//          page        -   Handle to the page. Returned by FPDF_LoadPage
-//          matrix      -   The transform matrix. It must be invertible.
-//          clipping    -   The rect to clip to.
+//          page        -   Handle to the page. Returned by FPDF_LoadPage.
+//          matrix      -   The transform matrix, which must be invertible.
+//                          See PDF Reference 1.7, 4.2.2 Common Transformations.
+//          clipping    -   The rect to clip to in page coords.
 //          flags       -   0 for normal display, or combination of the Page
 //                          Rendering flags defined above. With the FPDF_ANNOT
 //                          flag, it renders all annotations that do not require