diff --git a/doc/internals/buffer-ops.fig b/doc/internals/buffer-ops.fig
new file mode 100644
index 0000000..5cca1b6
--- /dev/null
+++ b/doc/internals/buffer-ops.fig
@@ -0,0 +1,152 @@
+#FIG 3.2
+Portrait
+Center
+Metric
+A4      
+100.00
+Single
+-2
+1200 2
+5 1 0 1 0 7 50 -1 -1 0.000 0 1 1 1 3133.105 2868.088 2385 3465 3150 3825 3915 3420
+	0 0 1.00 60.00 120.00
+	0 0 1.00 60.00 120.00
+5 1 0 1 0 7 50 -1 -1 0.000 0 0 1 1 3134.312 2832.717 2340 3420 3150 1845 3960 3375
+	0 0 1.00 60.00 120.00
+	0 0 1.00 60.00 120.00
+5 1 1 1 0 7 50 -1 -1 3.000 0 0 0 0 3150.000 2848.393 2115 3510 3150 1620 4185 3510
+5 1 0 1 0 7 50 -1 -1 0.000 0 1 1 1 3133.105 6423.088 2385 7020 3150 7380 3915 6975
+	0 0 1.00 60.00 120.00
+	0 0 1.00 60.00 120.00
+5 1 0 1 0 7 50 -1 -1 0.000 0 0 1 1 3134.312 6387.717 2340 6975 3150 5400 3960 6930
+	0 0 1.00 60.00 120.00
+	0 0 1.00 60.00 120.00
+5 1 1 1 0 7 50 -1 -1 3.000 0 0 0 0 3150.000 6403.393 2115 7065 3150 5175 4185 7065
+1 3 0 1 0 7 50 -1 -1 0.000 1 0.0000 3150 2835 1126 1126 3150 2835 3195 3960
+1 3 0 1 0 7 51 -1 -1 0.000 1 0.0000 3150 2835 1350 1350 3150 2835 4500 2835
+1 3 0 1 0 7 50 -1 -1 0.000 1 0.0000 3150 6390 1126 1126 3150 6390 3195 7515
+1 3 0 1 0 7 51 -1 -1 0.000 1 0.0000 3150 6390 1350 1350 3150 6390 4500 6390
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 0 0 2
+	 3150 3960 3150 4185
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 0 0 2
+	 4050 3510 4230 3690
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 0 0 2
+	 2250 3510 2070 3690
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 4410 3285 4455 3150
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 4500 2655 4455 2475
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 4185 1980 4050 1845
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 3645 1575 3510 1530
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 2295 1800 2160 1890
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 1980 2160 1935 2250
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 1800 2655 1800 2790
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 1800 3105 1845 3240
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 2877 1519 2697 1564
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 0 0 2
+	 3150 7515 3150 7740
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 0 0 2
+	 4050 7065 4230 7245
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 0 0 2
+	 2250 7065 2070 7245
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 4410 6840 4455 6705
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 4500 6210 4455 6030
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 4185 5535 4050 5400
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 3645 5130 3510 5085
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 2295 5355 2160 5445
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 1980 5715 1935 5805
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 1800 6210 1800 6345
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 1800 6660 1845 6795
+2 1 0 1 0 7 50 -1 -1 0.000 0 0 -1 1 0 2
+	1 1 1.00 60.00 120.00
+	 2877 5074 2697 5119
+3 0 0 1 0 7 50 -1 -1 0.000 0 1 0 4
+	1 1 1.00 60.00 120.00
+	 4950 3510 4635 3690 4545 3375 4185 3600
+	 0.000 1.000 1.000 0.000
+3 0 0 1 0 7 50 -1 -1 0.000 0 1 0 4
+	1 1 1.00 60.00 120.00
+	 2115 3600 1800 3330 1305 3285 1260 3780
+	 0.000 1.000 1.000 0.000
+3 0 0 1 0 7 50 -1 -1 0.000 0 1 0 3
+	1 1 1.00 60.00 120.00
+	 4635 2205 4545 1890 4185 2115
+	 0.000 1.000 0.000
+3 0 0 1 0 7 50 -1 -1 0.000 0 1 0 4
+	1 1 1.00 60.00 120.00
+	 4950 7065 4635 7245 4545 6930 4185 7155
+	 0.000 1.000 1.000 0.000
+3 0 0 1 0 7 50 -1 -1 0.000 0 1 0 4
+	1 1 1.00 60.00 120.00
+	 2115 7155 1800 6885 1305 6840 1260 7335
+	 0.000 1.000 1.000 0.000
+3 0 0 1 0 7 50 -1 -1 0.000 0 1 0 3
+	1 1 1.00 60.00 120.00
+	 4635 5760 4545 5445 4185 5670
+	 0.000 1.000 0.000
+4 1 0 50 -1 12 8 0.0000 4 75 75 3150 3690 l\001
+4 1 0 50 -1 12 8 0.0000 4 75 450 3150 2025 size-l\001
+4 1 0 50 -1 12 8 5.4978 4 45 75 1935 3780 w\001
+4 1 0 50 -1 12 8 0.7854 4 45 75 4365 3825 r\001
+4 1 0 50 -1 12 8 0.0000 4 90 300 3150 4365 (lr)\001
+4 1 0 50 -1 14 10 5.7596 4 90 270 2520 3960 OUT\001
+4 1 0 50 -1 12 8 5.7596 4 75 525 2430 4140 sendmax\001
+4 1 0 50 -1 14 10 0.5236 4 90 180 3690 4005 IN\001
+4 1 0 50 -1 12 8 0.5236 4 75 675 3870 4185 l-sendmax\001
+4 0 0 50 -1 12 8 0.0000 4 90 750 4545 2340 free space\001
+4 0 0 50 -1 12 8 0.0000 4 90 975 4950 3555  [eg: recv()]\001
+4 1 0 50 -1 12 8 0.0000 4 90 900 1260 4095 [eg: send()]\001
+4 1 0 50 -1 16 12 0.0000 4 165 2370 3150 855 Principle of the circular buffer\001
+4 1 0 50 -1 12 8 0.0000 4 90 600 1260 3960 buffer_*\001
+4 0 0 50 -1 12 8 0.0000 4 90 600 4950 3420 buffer_*\001
+4 1 0 50 -1 16 12 0.0000 4 165 1605 3150 1125 Current (since v1.3)\001
+4 0 0 50 -1 12 8 0.0000 4 90 1050 4950 6975 buffer_input_*\001
+4 1 0 50 -1 14 10 5.7596 4 90 270 2520 7515 OUT\001
+4 1 0 50 -1 14 10 0.5236 4 90 180 3690 7560 IN\001
+4 1 0 50 -1 12 8 0.0000 4 90 1125 1260 7515 buffer_output_*\001
+4 0 0 50 -1 12 8 0.0000 4 90 750 4545 5895 free space\001
+4 0 0 50 -1 12 8 0.0000 4 90 975 4950 7110  [eg: recv()]\001
+4 1 0 50 -1 12 8 0.0000 4 90 900 1260 7650 [eg: send()]\001
+4 0 0 50 -1 0 10 0.0000 4 135 1860 6075 1755 Some http_msg fields point to\001
+4 0 0 50 -1 0 10 0.0000 4 120 2175 6075 1950 absolute locations within the buffer,\001
+4 0 0 50 -1 0 10 0.0000 4 135 2040 6075 2145 making realignments quite tricky.\001
+4 0 0 50 -1 0 10 0.0000 4 135 1890 6075 5400 http_msg owns a pointer to the\001
+4 0 0 50 -1 0 10 0.0000 4 135 2055 6075 5595 struct_buffer and only uses offsets\001
+4 0 0 50 -1 0 10 0.0000 4 135 1095 6075 5790 relative to buf->p.\001
+4 1 0 50 -1 12 8 0.0000 4 75 600 3150 5760 size-i-o\001
+4 1 0 50 -1 12 8 0.0000 4 75 225 3150 7200 o+i\001
+4 1 0 50 -1 12 8 5.7596 4 45 75 2430 7695 o\001
+4 1 0 50 -1 12 8 0.5236 4 75 75 3870 7740 i\001
+4 1 0 50 -1 16 12 0.0000 4 180 1965 3150 4905 New design (1.5-dev9+)\001
+4 1 0 50 -1 12 8 0.0000 4 60 75 3150 7920 p\001