diff --git a/boot-programs/devices.hhp b/boot-programs/devices.hhp
index 9d198f8..ff12a9e 100644
--- a/boot-programs/devices.hhp
+++ b/boot-programs/devices.hhp
@@ -23,20 +23,65 @@
 
 // List interface.
 template <typename _T> //
-struct List : public Kernel::Cap:
-	List (Kernel::Cap c = Kernel::Cap ()) : Kernel::Cap (c):
-	// TODO
+struct List : public Kernel::Caps:
+	List (Kernel::Caps c = Kernel::Cap ()) : Kernel::Caps (c):
+	List <_T> create (unsigned size, Kernel::Memory mem = Kernel::my_memory):
+		return List <_T> (mem.create_caps (size))
+	void set (unsigned idx, _T value):
+		return Kernel::Caps::set (idx, value)
+	_T get (unsigned idx):
+		return _T (Kernel::Caps::get (idx))
 
+/// A block of data with a size and content.  Any character can be stored in it (including '\0').
 struct String : public Kernel::Cap:
 	String (Kernel::Cap c = Kernel::Cap ()) : Kernel::Cap (c):
-	// TODO
+	enum request:
+		GET_SIZE = 0x2001
+		GET_CHARS
+		GET_PAGE
+		_END_MARKER
+	/// Get the size of the string.
+	Kernel::Num get_size ():
+		return call (CAP_MASTER_DIRECT | GET_SIZE)
+	/// Get exactly 16 characters.  The index must be word-aligned.
+	char *get_chars (Kernel::Num idx, char buffer[16]):
+		call (CAP_MASTER_DIRECT | GET_CHARS, idx)
+		unsigned *b = (unsigned *)buffer
+		b[0] = Kernel::recv.data[0].l
+		b[1] = Kernel::recv.data[0].h
+		b[2] = Kernel::recv.data[1].l
+		b[3] = Kernel::recv.data[1].h
+		return buffer
+	/// Get a page from the string.  This need not be implemented for strings smaller than PAGE_SIZE.  The index must be page-aligned.
+	Cap get_page (Kernel::Num idx, Kernel::Page ret = Kernel::my_memory.create_page ()):
+		ocall (ret, CAP_MASTER_DIRECT | GET_PAGE, idx)
+		return ret
+
+/// A writable String.
+struct WString : public String:
+	WString (Kernel::Cap c = Kernel::Cap ()) : String (c):
+	enum request:
+		TRUNCATE = String::_END_MARKER
+		SET_CHARS
+		SET_PAGE
+		_END_MARKER
+	/// Set the size of the string.  Strings may have a limit to this setting.
+	void truncate (Kernel::Num size):
+		call (CAP_MASTER_DIRECT | TRUNCATE, size)
+	/// Set exactly 4 characters.  The index must be word-aligned.
+	void set_chars (Kernel::Num idx, char buffer[4]):
+		call (Kernel::Num (CAP_MASTER_DIRECT | SET_CHARS, *(unsigned *)buffer), idx)
+	/// Overwrite a page from the string.  This need not be implemented for strings smaller than PAGE_SIZE.  The index must be page-aligned.  The caller may lose the frame in the transaction.
+	void set_page (Kernel::Num idx, Kernel::Page page):
+		ocall (page, CAP_MASTER_DIRECT | SET_PAGE, idx)
 
 // Keyboard interface.
 struct Keyboard : public Kernel::Cap:
 	Keyboard (Kernel::Cap c = Kernel::Cap ()) : Kernel::Cap (c):
 	enum request:
-		SET_CB = 1
+		SET_CB = WString::_END_MARKER
 		GET_KEYS
+		_END_MARKER
 	// At event: the callback is called with a keycode.  One bit defines if it's a press or release event.
 	enum constant:
 		RELEASE = 1 << 31
@@ -46,16 +91,17 @@ struct Keyboard : public Kernel::Cap:
 	// Get a list of keys on this keyboard.  The key codes start at zero with no gaps.
 	List <String> get_keys ():
 		icall (CAP_MASTER_DIRECT | GET_KEYS)
-		return Kernel::get_arg ()
+		return List <String> (Kernel::get_arg ())
 
 // Display interface.
 struct Display : public Kernel::Cap:
 	Display (Kernel::Cap c = Kernel::Cap ()) : Kernel::Cap (c):
 	enum request:
-		EOF_CB = 1
+		EOF_CB = Keyboard::_END_MARKER
 		CREATE_FB
 		USE_FB
 		GET_INFO
+		_END_MARKER
 	// Register an end-of-frame callback.
 	// At end of frame, the callback is invoked and forgotten.  It must be reregistered to keep a stream of events.
 	void set_eof_cb (Kernel::Cap cb):
@@ -83,9 +129,10 @@ struct Display : public Kernel::Cap:
 struct File : public Kernel::Cap:
 	File (Kernel::Cap c = Kernel::Cap ()) : Kernel::Cap (c):
 	enum request:
-		INFO = 1
+		INFO = Display::_END_MARKER
 		CLOSE
 		MAP_HANDLE
+		_END_MARKER
 	// Get information about the file.
 	Kernel::Num get_info (unsigned type):
 		return icall (Kernel::Num (CAP_MASTER_DIRECT | INFO, type))
@@ -101,12 +148,13 @@ struct File : public Kernel::Cap:
 struct Directory : public File:
 	Directory (Kernel::Cap c = Kernel::Cap ()) : File (c):
 	enum request:
-		GET_SIZE = 1
+		GET_SIZE = File::_END_MARKER
 		GET_NAME
 		GET_FILE
 		GET_FILE_INFO
 		CREATE_FILE
 		DELETE_FILE
+		_END_MARKER
 	// Get the number of entries in this directory.
 	Kernel::Num get_size ():
 		return call (CAP_MASTER_DIRECT | GET_SIZE)
@@ -133,8 +181,9 @@ struct Directory : public File:
 struct Stream : public File:
 	Stream (Kernel::Cap c = Kernel::Cap ()) : File (c):
 	enum request:
-		READ = 1
+		READ = Directory::_END_MARKER
 		WRITE
+		_END_MARKER
 	// Try to read size bytes.  Returns the number of bytes successfully read.
 	Kernel::Num read (Kernel::Num size):
 		return icall (CAP_MASTER_DIRECT | READ, size)
@@ -146,9 +195,10 @@ struct Stream : public File:
 struct Seekable : public File:
 	Seekable (Kernel::Cap c = Kernel::Cap ()) : File (c):
 	enum request:
-		READ = 1
+		READ = Stream::_END_MARKER
 		WRITE
 		TRUNCATE
+		_END_MARKER
 	// Try to read size bytes from position idx.  Returns the number of bytes successfully read.
 	Kernel::Num read (Kernel::Num idx, unsigned size):
 		return icall (Kernel::Num (CAP_MASTER_DIRECT | READ, size), idx)
diff --git a/invoke.ccp b/invoke.ccp
index c00616a..f7d8520 100644
--- a/invoke.ccp
+++ b/invoke.ccp
@@ -708,6 +708,16 @@ static void print_cap (kCapRef cap, kCapRef self):
 static void caps_invoke (unsigned cmd, unsigned target, Kernel::Num protected_data, kCapability::Context *c):
 	kCaps *caps = (kCapsP)protected_data.l
 	switch cmd:
+		case Kernel::Caps::GET & REQUEST_MASK:
+			if c->data[1].l >= caps->size:
+				dpanic (0, "invalid index for get caps")
+				return
+			kCapability *ret = caps->cap (c->data[1].l)
+			reply_cap ((unsigned)ret->target, ret->protected_data, ((unsigned)ret->target & ~KERNEL_MASK) == 0 ? &((kObject *)ret->target)->refs : &ret->target->capabilities)
+			return
+		case Kernel::Caps::GET_SIZE & REQUEST_MASK:
+			reply_num (caps->size)
+			return
 		case Kernel::Caps::SET & REQUEST_MASK:
 			if c->data[1].l >= caps->size:
 				dpanic (0, "invalid index for set caps")
@@ -715,6 +725,9 @@ static void caps_invoke (unsigned cmd, unsigned target, Kernel::Num protected_da
 			caps->clone (c->data[1].l, c->arg, c->copy[1])
 			reply_num (0)
 			return
+		case Kernel::Caps::TRUNCATE & REQUEST_MASK:
+			dpanic (0, "truncate caps is not implemented yet.")
+			return
 		case Kernel::Caps::PRINT & REQUEST_MASK:
 			if c->data[1].l >= caps->size:
 				dpanic (0, "invalid caps for print")
diff --git a/iris.hhp b/iris.hhp
index bd654ec..394a728 100644
--- a/iris.hhp
+++ b/iris.hhp
@@ -353,12 +353,22 @@ namespace Kernel:
 		enum request:
 			// Not an operation; this capability can be used in Thread::USE_SLOT.
 			USE = CAPTYPE_CAPS + 1
+			GET
+			GET_SIZE
 			SET
+			TRUNCATE
 			PRINT
 		unsigned use (unsigned slot = alloc_slot ()):
 			return my_thread.use (*this, slot)
+		Cap get (unsigned idx):
+			call (CAP_MASTER_DIRECT | GET, idx)
+			return get_arg ()
+		unsigned get_size ():
+			return call (CAP_MASTER_DIRECT | GET_SIZE).l
 		void set (unsigned idx, Cap cap):
 			ocall (cap, CAP_MASTER_DIRECT | SET, idx)
+		void truncate (unsigned new_size):
+			call (CAP_MASTER_DIRECT | TRUNCATE, new_size)
 		void print (unsigned idx):
 			invoke (CAP_MASTER_DIRECT | PRINT, idx)
 
diff --git a/plan b/plan
index 3560761..5e9608e 100644
--- a/plan
+++ b/plan
@@ -1,5 +1,2 @@
-kernel capabilities: 1 per aktie; bevat code in plaats van bitmask.  CREATE ipv DEGRADE.
-protected data in receiver
-message: a0-a3: data0; data1; protectedL; protectedH
 caps zonder size limit?
 invoke ipc: try sync; try receiver memory; try caller memory; fail.