diff --git a/TODO.md b/TODO.md
index d9b244f..440e41a 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,4 +1,8 @@
 # TODO in libg1m
+## Things
+- Implement the 'in case of error, finish reading the file so that the
+  provided stream is usable' behaviour?
+
 ## Find out what these formats are/how to parse them
 - G3M (like G1M?);
 - G1K/G3K (keys?).
diff --git a/doc/g1m_error.3.txt b/doc/g1m_error.3.txt
index b40bd1e..fc0694b 100644
--- a/doc/g1m_error.3.txt
+++ b/doc/g1m_error.3.txt
@@ -32,6 +32,8 @@ the code of the error that happened. The error codes are the following:
 	Provided or generated stream was *NULL*.
 *g1m_error_noread*::
 	Stream was not readable.
+*g1m_error_wrong_type*::
+	The found type was not the expected type.
 *g1m_error_magic*::
 	File might be corrupted.
 *g1m_error_eof*::
diff --git a/doc/g1m_open.3.txt b/doc/g1m_open.3.txt
index 50860de..89524cb 100644
--- a/doc/g1m_open.3.txt
+++ b/doc/g1m_open.3.txt
@@ -15,17 +15,27 @@ SYNOPSIS
 ----
 #include <libg1m.h>
 
-int g1m_open(g1m_t **handle, const char *path);
-int g1m_fopen(g1m_t **handle, FILE *stream);
+int g1m_open(g1m_t **handle, const char *path,
+	g1m_type_t expected_types);
+int g1m_fopen(g1m_t **handle, FILE *stream,
+	g1m_type_t expected_types);
 ----
 
 DESCRIPTION
 -----------
 Open and decode a file. If everything goes well, the handle is stored at
-**handle*.
+**handle*. If you are expecting one or more types in particular, set
+*expected_types* to the OR'd types (e.g. _g1m_type_mcs | g1m_type_storage_),
+then, if the wrong type is found, the file will not be decoded to the end,
+only to the point where it can be identified. If you aren't expecting any
+type in particular, set *expected_types* to zero.
 
-For *g1m_fopen*, the stream only requires reading (writing and seeking
-capabilities are not required).
+*g1m_open* will open the file at the given path, decode it, and close it,
+whereas *g1m_fopen* will take an opened stream (with libc) and will not
+close it. Only reading is required (writing and seeking capabilities are
+not). In case of a decoding error (magic problem, memory allocation error,
+...), the stream is unusable as the number of read bytes by libg1m is not
+known.
 
 RETURN VALUE
 ------------