WinComm/forms

Remote Forms System

A remote GUI system for Windows 3.1. Forms are designed visually in Delphi 1.0's IDE, converted to a text protocol by a Linux tool, and served to a Delphi 1.0 client over serial. The client creates native Windows 3.1 controls and sends user events back to the server.

Architecture

  Linux                            Serial              Windows 3.1
 +-----------------+         +----------------+     +------------------+
 | Delphi IDE      |         |                |     |                  |
 | design → .DFM   |         |   Transport    |     |  TFormClient     |
 |        |        |         |  (newline-     |     |  creates native  |
 |    dfm2form     |         |  delimited)    |     |  controls from   |
 |        |        |         |                |     |  commands, sends |
 |    .form file   |         |  Server -----> |---->|  events back     |
 |        |        |         |  commands      |     |                  |
 |  FormServerT    |         |                |     |                  |
 |  loads .form,   |         |  <----- Client |<----|                  |
 |  sends commands |         |  events        |     |                  |
 +-----------------+         +----------------+     +------------------+

Components

File	Language	Platform	Purpose
dfm2form.c	C	Linux	Converts binary DFM to .form text
formsrv.h	C	Linux	Server library header
formsrv.c	C	Linux	Server library implementation
formcli.pas	Pascal	Win 3.1	Client form engine (Delphi 1.0)
protocol.md	—	—	Protocol specification

Building

make              # builds dfm2form and formsrv.o
make clean        # removes build artifacts

Requires GCC on Linux. The Delphi unit (formcli.pas) is compiled as part of a Delphi 1.0 project on Windows.

DFM Converter

dfm2form reads Delphi 1.0 binary DFM files (TPF0 format) and outputs .form files containing protocol commands. The form ID in the output is a placeholder (0); the server assigns a dynamic ID when it streams the file to the client.

dfm2form <input.dfm> [output.form]

Examples:

dfm2form login.dfm                    # output to stdout
dfm2form login.dfm login.form         # output to file

Output is a sequence of protocol commands:

FORM.CREATE 0 400 300 "Login"
CTRL.CREATE 0 1 Label 20 20 100 17 Caption="Username:"
CTRL.CREATE 0 2 Edit 120 18 200 21 Text="" MaxLength=32 TabOrder=0
CTRL.CREATE 0 3 Label 20 52 100 17 Caption="Password:"
CTRL.CREATE 0 4 Edit 120 50 200 21 Text="" MaxLength=32 TabOrder=1
CTRL.CREATE 0 5 Button 245 90 75 25 Caption="OK" TabOrder=2
CTRL.CREATE 0 6 Button 160 90 75 25 Caption="Cancel" TabOrder=3
EVENT.BIND 0 5 Enter
FORM.SHOW 0

The placeholder 0 IDs are replaced at runtime by formServerSendForm.

The converter maps Delphi class names to protocol control types, extracts geometry and properties, and emits EVENT.BIND for any event handler assignments in the DFM that are not auto-wired (see Events below). Unknown control classes are skipped with a warning.

Server Library (C)

The server streams .form files from disk to a remote client through a pluggable transport interface, assigning dynamic form IDs. It also receives events from the client and dispatches them to a callback.

Transport Interface

Implement FormTransportT to connect the server to your communication channel:

typedef struct {
    int  (*readMessage)(char *buf, int32_t maxLen, void *ctx);
    void (*writeMessage)(const char *buf, void *ctx);
    void *ctx;
} FormTransportT;

• readMessage — Read one complete message into buf. Return the number of bytes read, or 0 if no message is available. Must not block.
• writeMessage — Send a null-terminated message string. The transport adds framing (e.g., CR+LF for serial).
• ctx — Opaque pointer passed through to both callbacks.

API

// Create/destroy
FormServerT *formServerCreate(FormTransportT *transport);
void         formServerDestroy(FormServerT *server);

// Stream a .form file to the client, assigning a dynamic form ID.
// Returns the assigned form ID, or -1 on error.
int32_t      formServerSendForm(FormServerT *server, const char *path);

// Form visibility
void         formServerShowForm(FormServerT *server, int32_t formId);
void         formServerHideForm(FormServerT *server, int32_t formId);

// Destroy a form on the client.
void         formServerDestroyForm(FormServerT *server, int32_t formId);

// Update a control property
void         formServerSetProp(FormServerT *server, int32_t formId,
                               int32_t ctrlId, const char *prop,
                               const char *value);

// Bind/unbind opt-in events
void         formServerBindEvent(FormServerT *server, int32_t formId,
                                 int32_t ctrlId, const char *eventName);
void         formServerUnbindEvent(FormServerT *server, int32_t formId,
                                   int32_t ctrlId, const char *eventName);

// Set event callback
void         formServerSetEventCallback(FormServerT *server,
                                        EventCallbackT cb, void *userData);

// Poll for one incoming event.  Returns true if an event was processed.
bool         formServerPollEvent(FormServerT *server);

Event Callback

typedef void (*EventCallbackT)(int32_t formId, int32_t ctrlId,
                               const char *eventName, const char *data,
                               void *userData);

• formId / ctrlId — Identify which control fired the event.
• eventName — "Click", "Change", "Select", etc.
• data — Event-specific data (may be empty). See the Events section below for formats.

Server Example

#include "formsrv.h"

void onEvent(int32_t formId, int32_t ctrlId, const char *eventName, const char *data, void *userData) {
    printf("Event: form=%d ctrl=%d event=%s data=%s\n",
           formId, ctrlId, eventName, data);

    FormServerT *server = (FormServerT *)userData;

    // React to a button click by updating a label
    if (ctrlId == 5 && strcmp(eventName, "Click") == 0) {
        formServerSetProp(server, formId, 1, "Caption", "\"Clicked!\"");
    }
}

int main(void) {
    FormTransportT transport = { myReadFn, myWriteFn, myCtx };
    FormServerT *server = formServerCreate(&transport);

    formServerSetEventCallback(server, onEvent, server);

    int32_t formId = formServerSendForm(server, "login.form");

    // Main loop
    while (running) {
        formServerPollEvent(server);
    }

    formServerDestroy(server);
    return 0;
}

Client Engine (Delphi 1.0)

The client receives protocol commands, creates native Windows 3.1 controls, and sends user events back through the transport.

Transport Interface

Subclass TFormTransport to provide your communication channel:

TFormTransport = class(TObject)
public
  function ReadMessage(Buf: PChar; BufSize: Integer): Integer; virtual; abstract;
  procedure WriteMessage(Buf: PChar; Len: Integer); virtual; abstract;
end;

• ReadMessage — Read one complete message into Buf. Return the number of bytes read, or 0 if no message is available.
• WriteMessage — Send Len bytes from Buf as a complete message.

PChar-based (not short strings) to handle messages up to 4096 bytes.

Serial Transport Example

TSerialTransport = class(TFormTransport)
private
  FComm:    TKPComm;
  FRecvBuf: array[0..4095] of Char;
  FRecvLen: Integer;
public
  function ReadMessage(Buf: PChar; BufSize: Integer): Integer; override;
  procedure WriteMessage(Buf: PChar; Len: Integer); override;
end;

function TSerialTransport.ReadMessage(Buf: PChar; BufSize: Integer): Integer;
var
  S:   string;
  I:   Integer;
  Len: Integer;
begin
  Result := 0;
  { Accumulate serial data }
  S := FComm.Input;
  if Length(S) > 0 then
  begin
    Move(S[1], FRecvBuf[FRecvLen], Length(S));
    Inc(FRecvLen, Length(S));
  end;
  { Scan for newline }
  for I := 0 to FRecvLen - 1 do
  begin
    if FRecvBuf[I] = #10 then
    begin
      Len := I;
      if (Len > 0) and (FRecvBuf[Len - 1] = #13) then
        Dec(Len);
      if Len > BufSize - 1 then
        Len := BufSize - 1;
      Move(FRecvBuf, Buf^, Len);
      Buf[Len] := #0;
      { Shift remainder }
      Move(FRecvBuf[I + 1], FRecvBuf, FRecvLen - I - 1);
      Dec(FRecvLen, I + 1);
      Result := Len;
      Exit;
    end;
  end;
end;

procedure TSerialTransport.WriteMessage(Buf: PChar; Len: Integer);
var
  Msg: string;
begin
  Msg := StrPas(Buf) + #13#10;
  FComm.Output := Msg;
end;

Using TFormClient

var
  Transport: TSerialTransport;
  Client:    TFormClient;

{ Setup }
Transport := TSerialTransport.Create;
Transport.FComm := KPComm1;   { your TKPComm instance }
Client := TFormClient.Create(Transport);

{ Main loop (PeekMessage style) }
while not Terminated do
begin
  while PeekMessage(Msg, 0, 0, 0, PM_REMOVE) do
  begin
    TranslateMessage(Msg);
    DispatchMessage(Msg);
  end;
  Client.ProcessMessages;   { pumps incoming commands }
  Yield;
end;

{ Cleanup }
Client.Free;
Transport.Free;

ProcessMessages calls ReadMessage in a loop until no more messages are available, dispatching each command as it arrives.

Supported Controls

Type	Delphi Class	Description
Label	TLabel	Static text label
Edit	TEdit	Single-line text input
Button	TButton	Push button
CheckBox	TCheckBox	Check box with label
ListBox	TListBox	Scrollable list of items
ComboBox	TComboBox	Drop-down list with text input
Memo	TMemo	Multi-line text input
Image	TImage	Bitmap image display (BMP only)
GroupBox	TGroupBox	Cosmetic grouping frame
RadioButton	TRadioButton	Radio button (one group/form)
Panel	TPanel	Cosmetic container panel
ScrollBar	TScrollBar	Horizontal or vertical scrollbar
MediaPlayer	TMediaPlayer	MCI media player control
MainMenu	TMainMenu	Form main menu bar
PopupMenu	TPopupMenu	Context (right-click) menu
MenuItem	TMenuItem	Menu item (child of menu)
RadioGroup	TRadioGroup	Grouped radio buttons
BitBtn	TBitBtn	Button with bitmap glyph
SpeedButton	TSpeedButton	Flat toolbar-style button
TabSet	TTabSet	Tab strip (no pages)
Notebook	TNotebook	Multi-page container
TabbedNotebook	TTabbedNotebook	Tabbed multi-page container
MaskEdit	TMaskEdit	Masked text input
Outline	TOutline	Hierarchical tree list
Bevel	TBevel	Cosmetic beveled line/box
Header	THeader	Column header bar
ScrollBox	TScrollBox	Scrollable container
StringGrid	TStringGrid	Editable string grid

Creating Controls

Controls are created with CTRL.CREATE, specifying position, size, and optional inline properties:

CTRL.CREATE <formId> <ctrlId> <type> <left> <top> <width> <height> [Key="val" ...]

Example:

CTRL.CREATE 1 3 Edit 120 50 200 21 Text="hello" MaxLength=32 TabOrder=1

Control IDs are positive integers assigned by the server. They must be unique within a form.

Updating Controls

Properties can be changed at any time after creation with CTRL.SET:

CTRL.SET <formId> <ctrlId> Key="val" [Key="val" ...]

Example:

CTRL.SET 1 3 Text="world" Enabled=0

Properties

Common Properties

These properties apply to all or most controls:

Property	Format	Description
Enabled	0 or 1	Disable or enable the control
Visible	0 or 1	Hide or show the control
TabOrder	Integer	Keyboard tab order within the form (all windowed controls except Label and Image)
PopupMenu	Integer (ctrlId of PopupMenu)	Associates a right-click context menu with the control

Label, Button, GroupBox

Property	Format
Caption	Quoted string

The display text for the control.

Example: Caption="Submit"

Edit

Property	Format	Description
Text	Quoted string	Editable text content
MaxLength	Integer	Max characters (0 = no limit)
ReadOnly	0 or 1	Prevent user editing when enabled

Example: Text="Hello world" MaxLength=50

CheckBox, RadioButton

Property	Format	Description
Caption	Quoted string	Display text
Checked	0 or 1	Checked or unchecked

Example: Caption="Accept terms" Checked=1

ListBox

Property	Format	Description
Items	Quoted string (\n-delimited)	Item list
ItemIndex	Integer (-1 = none)	Selected item

Replaces the entire item list. The control is cleared before the new items are added.

Example: Items="Red\nGreen\nBlue" ItemIndex=0

ComboBox

Property	Format	Description
Text	Quoted string	Editable text
Items	Quoted string (\n-delimited)	Drop-down items
ItemIndex	Integer (-1 = none)	Selected item

Example: Items="Red\nGreen\nBlue" ItemIndex=1

Memo

Property	Format	Description
Text	Quoted string (\n for line breaks)	Text content
ReadOnly	0 or 1	Prevent editing
ScrollBars	Integer 0-3	Scroll bar style

ScrollBars values:

• 0 — ssNone (no scroll bars)
• 1 — ssHorizontal
• 2 — ssVertical
• 3 — ssBoth

Example:

CTRL.SET 1 5 Text="Line one\nLine two\nLine three" ScrollBars=2

Image

Property	Format	Description
Picture	Quoted string (filename)	BMP file to display
Stretch	0 or 1	Stretch to fill bounds
Center	0 or 1	Center within bounds
Transparent	0 or 1	Transparent background

Picture path is resolved relative to the client's BasePath setting. Subdirectories are allowed. Only BMP files are supported.

Example: Picture="images\logo.bmp" Stretch=1

Note: dfm2form does not emit Picture from DFM files because image data is stored as a binary blob in the DFM. Set Picture at runtime via CTRL.SET or by manually editing the .form file.

Panel

Property	Format	Description
Caption	Quoted string	Display text
BevelOuter	Integer 0-2	Outer bevel
BevelInner	Integer 0-2	Inner bevel
BorderStyle	0 or 1	Border

Bevel values: 0 (bvNone), 1 (bvLowered), 2 (bvRaised). BorderStyle values: 0 (bsNone), 1 (bsSingle).

Example: BevelOuter=2 BevelInner=1 BorderStyle=0

ScrollBar

Property	Format	Description
Kind	Integer	0 (sbHorizontal), 1 (sbVertical)
Min	Integer	Minimum value
Max	Integer	Maximum value
Position	Integer	Current position
LargeChange	Integer	Change on track click
SmallChange	Integer	Change on arrow click

Example: Kind=1 Min=0 Max=100 Position=50 LargeChange=10 SmallChange=1

MediaPlayer

Property	Format	Description
FileName	Quoted string	Media file path
DeviceType	Quoted string	MCI device type
AutoOpen	0 or 1	Open file automatically
Command	Quoted string	Pseudo-property (triggers method)

FileName path is resolved relative to the client's BasePath setting.

DeviceType values: dtAutoSelect, dtAVIVideo, dtCDAudio, dtDAT, dtDigitalVideo, dtMMMovie, dtOther, dtOverlay, dtScanner, dtSequencer, dtVCR, dtVideodisc, dtWaveAudio.

Command triggers a method call instead of setting a value. Valid commands: Open, Play, Stop, Close, Pause, Resume, Rewind, Next, Previous.

Example: FileName="sounds\intro.wav" DeviceType="dtWaveAudio" AutoOpen=1

MainMenu, PopupMenu

No type-specific properties. One MainMenu per form (auto-attached). PopupMenu is associated with any control via the common PopupMenu property.

MenuItem

Property	Format	Description
Caption	Quoted string	Menu item text
Parent	Integer	ctrlId of parent menu/item
Checked	0 or 1	Check mark
ShortCut	Integer	Delphi ShortCut value

ShortCut uses Delphi's encoding (virtual key + modifier flags).

Example: Caption="&Open" Parent=2 ShortCut=16463

RadioGroup

Property	Format	Description
Caption	Quoted string	Group label
Items	Quoted string (\n-delimited)	Radio button labels
ItemIndex	Integer (-1 = none)	Selected item
Columns	Integer	Column count

Example: Caption="Color" Items="Red\nGreen\nBlue" Columns=2 ItemIndex=0

BitBtn

Property	Format	Description
Caption	Quoted string	Button text
Kind	Integer 0-10	Predefined button kind
Layout	Integer 0-3	Glyph position
NumGlyphs	Integer 1-4	Glyph images in bitmap

Kind values: 0 (bkCustom), 1 (bkOK), 2 (bkCancel), 3 (bkHelp), 4 (bkYes), 5 (bkNo), 6 (bkClose), 7 (bkAbort), 8 (bkRetry), 9 (bkIgnore), 10 (bkAll).

Layout values: 0 (blGlyphLeft), 1 (blGlyphRight), 2 (blGlyphTop), 3 (blGlyphBottom).

NumGlyphs: number of glyph images (up, disabled, clicked, down).

Example: Caption="OK" Kind=1 Layout=0 NumGlyphs=2

SpeedButton

Property	Format	Description
Caption	Quoted string	Button text
Layout	Integer 0-3	Glyph position
NumGlyphs	Integer 1-4	Glyph images in bitmap
GroupIndex	Integer	Radio group (0 = no group)
Down	0 or 1	Pressed state
AllowAllUp	0 or 1	Allow all buttons unpressed

Layout values: 0 (blGlyphLeft), 1 (blGlyphRight), 2 (blGlyphTop), 3 (blGlyphBottom).

Speed buttons with the same non-zero GroupIndex act as a radio group. Down is only meaningful when GroupIndex is non-zero.

Example: GroupIndex=1 Down=1 AllowAllUp=0

TabSet, Notebook, TabbedNotebook

Property	Format	Description
Items	Quoted string (\n-delimited)	Tab/page list
ItemIndex	Integer (-1 = none)	Active tab

Example: Items="General\nAdvanced\nAbout" ItemIndex=0

MaskEdit

Property	Format	Description
Text	Quoted string	Editable text content
MaxLength	Integer	Max characters (0 = no limit)
EditMask	Quoted string	Input mask (mask;save;blank char)

Example: EditMask="(999) 000-0000;1;_"

Outline

Property	Format	Description
Items	Quoted string (\n-delimited)	Tree items
OutlineStyle	Integer 0-6	Display style

OutlineStyle values:

• 0 — osText
• 1 — osPlusMinusText
• 2 — osPlusMinus
• 3 — osPictureText
• 4 — osPicturePlusMinusText
• 5 — osTreeText
• 6 — osTreePictureText

Example: OutlineStyle=5

Bevel

Property	Format	Description
Shape	Integer 0-5	Bevel shape
Style	0 or 1	Lowered/raised

Shape values:

• 0 — bsBox
• 1 — bsFrame
• 2 — bsTopLine
• 3 — bsBottomLine
• 4 — bsLeftLine
• 5 — bsRightLine

Style values: 0 (bsLowered), 1 (bsRaised).

Example: Shape=2 Style=1

Header

Property	Format	Description
Items	Quoted string (\n-delimited)	Section headers

Example: Items="Name\nAge\nCity"

ScrollBox

No type-specific properties.

StringGrid

Property	Format	Description
ColCount	Integer (default 5)	Number of columns
RowCount	Integer (default 5)	Number of rows
FixedCols	Integer (default 1)	Non-scrollable left cols
FixedRows	Integer (default 1)	Non-scrollable top rows
DefaultColWidth	Integer (pixels)	Default column width
DefaultRowHeight	Integer (pixels)	Default row height
Options	Integer (bitmask)	Grid options
Cells	Quoted string (tab-delimited cols, \n-delimited rows)	Bulk-load all cells
Cell	Quoted string (col,row,value)	Set a single cell

Options bitmask of TGridOption values:

Bit	Value	Option	Description
0	0x0001	goFixedVertLine	Vertical lines on fixed
1	0x0002	goFixedHorzLine	Horizontal lines on fixed
2	0x0004	goVertLine	Vertical lines on cells
3	0x0008	goHorzLine	Horizontal lines on cells
4	0x0010	goRangeSelect	Allow range selection
5	0x0020	goDrawFocusSelected	Draw focused cell selected
6	0x0040	goRowSizing	Allow row resizing
7	0x0080	goColSizing	Allow column resizing
8	0x0100	goRowMoving	Allow row moving
9	0x0200	goColMoving	Allow column moving
10	0x0400	goEditing	Allow in-place editing
11	0x0800	goTabs	Tab between cells
12	0x1000	goThumbTracking	Track scrollbar thumb

Cells is a bulk-load property: columns are separated by tab characters, rows by newlines. Row 0 is the first row (typically fixed header). Cell sets a single cell value: column and row are zero-based indices.

Example: Cells="Name\tAge\nAlice\t30\nBob\t25"

Example: Cell="1,2,Hello"

BasePath

BasePath is a property on TFormClient (not a protocol property). Set it before loading forms to specify where file-based properties (Picture, FileName) resolve relative paths. Example:

Client.BasePath := 'C:\MYAPP';

A Picture value of "images\logo.bmp" then resolves to C:\MYAPP\images\logo.bmp.

Events

Auto-wired Events

These events are automatically connected when a control is created. No EVENT.BIND command is needed.

Control Type	Event	Data Sent
Button	Click	(none)
CheckBox	Click	(none)
RadioButton	Click	(none)
Edit	Change	"new text"
Memo	Change	"new text"
ScrollBar	Change	<position>
ListBox	Select	<index> "selected text"
ComboBox	Select	<index> "selected text"
ComboBox	Change	"new text"
MenuItem	Click	(none)
RadioGroup	Click	<itemIndex>
BitBtn	Click	(none)
SpeedButton	Click	(none)
TabSet	Change	<tabIndex>
TabbedNotebook	Change	<pageIndex>
MaskEdit	Change	"new text"
StringGrid	SelectCell	<col> <row>

Opt-in Events

These events require an explicit EVENT.BIND command before the client will send them. Use EVENT.UNBIND to disconnect.

Event	Data Sent	Notes
Click	(none)	Image, GroupBox, Panel only
DblClick	(none)	Double-click on any control
Notify	(none)	MediaPlayer playback notification
KeyDown	<vkCode>	Windows virtual key code
KeyUp	<vkCode>	Windows virtual key code
Enter	(none)	Control received focus
Exit	(none)	Control lost focus
MouseDown	<x> <y> <button>	0=left, 1=right, 2=middle
MouseUp	<x> <y> <button>	0=left, 1=right, 2=middle
MouseMove	<x> <y> 0	Coordinates relative to control
SetEditText	<col> <row> "text"	StringGrid in-place edit

Form Close Event

When the user clicks the form's close button, the client sends:

EVENT <formId> 0 Close

The form is not automatically destroyed. The server must send FORM.DESTROY to close it, or FORM.HIDE to hide it, or ignore the event to keep it open.

Event Message Format

All events from client to server follow this format:

EVENT <formId> <ctrlId> <eventName> [<data>]

Binding Example

EVENT.BIND 1 3 KeyDown        (server sends)
EVENT 1 3 KeyDown 13           (client sends back when Enter pressed)
EVENT.UNBIND 1 3 KeyDown      (server disconnects)

Menu Hierarchy Example

Menus are built using flat CTRL.CREATE commands with Parent properties to establish the hierarchy:

CTRL.CREATE 1 1 MainMenu 0 0 0 0
CTRL.CREATE 1 2 MenuItem 0 0 0 0 Caption="&File" Parent=1
CTRL.CREATE 1 3 MenuItem 0 0 0 0 Caption="&Open" Parent=2 ShortCut=16463
CTRL.CREATE 1 4 MenuItem 0 0 0 0 Caption="&Save" Parent=2 ShortCut=16467
CTRL.CREATE 1 5 MenuItem 0 0 0 0 Caption="E&xit" Parent=2
CTRL.CREATE 1 6 MenuItem 0 0 0 0 Caption="&Help" Parent=1
CTRL.CREATE 1 7 MenuItem 0 0 0 0 Caption="&About" Parent=6

This creates a menu bar with File (Open, Save, Exit) and Help (About). MenuItem ctrl 2 is a child of MainMenu ctrl 1; ctrl 3-5 are children of the File item (ctrl 2); ctrl 7 is a child of the Help item (ctrl 6).

String Encoding

All strings in the protocol are double-quoted. The following escape sequences are recognized:

Escape	Character
\"	Literal "
\\	Literal \
\n	Newline (LF)
\r	Carriage return
\t	Tab

Transport Layer

The protocol is transport-agnostic. Both the C server and Delphi client communicate through abstract interfaces that deliver whole messages. The current implementation uses newline-delimited serial (CR+LF framing), but the transport can be replaced without changing any protocol or application code.

Requirements

• ReadMessage must be non-blocking (return 0 if no data).
• WriteMessage sends one complete message per call.
• Transport handles framing — the protocol layer never sees delimiters.

Limitations

• RadioButton grouping: All RadioButtons on a form belong to one group. Use RadioGroup for multiple independent radio groups per form.
• Image format: Only BMP files are supported for the Picture property.
• dfm2form and Picture: The converter cannot extract image filenames from DFM files (image data is stored as a binary blob). Set Picture at runtime via CTRL.SET or by manually editing the .form file.
• GroupBox and Panel: These are cosmetic-only containers. The protocol has no child containment — all controls are direct children of the form.

Limits

Limit	Value
Max message length	4096 bytes
Max controls per form	256
Form ID range	1-65535 (stored in high word of Tag)
Control ID range	1-65535 (stored in low word of Tag)