The Posn property specifies the location of the internal top-left corner of the window relative to the top-left corner of the screen. If the window has a title bar and/or border, you must allow sufficient space for them. Similarly, the Size property specifies the internal size of the window excluding the title bar and border. The default for Size is 50% of the screen height and width. The default for Posn places the Form in the middle of the screen.

Normally, a Form has a title bar, a system menu box, a border and maximise and minimise buttons. To disable the System Menu box, set SysMenu to 0. To disable one or both of the maximise/minimise buttons, set MaxButton and/or MinButton to 0.

The HelpButton property specifies that a Question (?) button appears in the title bar of the Form. However, this does not apply if the Form has a maximise or minimise button which both take precedence. The user may obtain help by clicking on the Question (?) button and then on a control in the Form. It is up to you to provide the help by responding to the Help event on the control.

By default, a Form may be moved and resized using the mouse. These actions are achieved by dragging on the title bar and border respectively. It follows that a Form that is Moveable must have a title bar, and one that is Sizeable must have a border, regardless of the value of other properties. Also, if you specify any of SysMenu, MaxButton or MinButton, the window must have a title bar in which to place these controls. A title bar itself requires a border. To obtain a window without a title bar, you must therefore set Moveable, SysMenu, MaxButton and MinButton to 0. Note that setting Caption does not force a title bar on the window.

If Sizeable is 1, the window will have a double-line border, regardless of the values of other properties. If Sizeable is 0, and any one or more of Moveable, SysMenu, MaxButton, MinButton or Border is 1, the window will have a 1-pixel border. Only if all these properties are 0 will the window be borderless. To obtain a dialog box that may only be moved or closed, set Border to 2.

Note that the default value for Caption is an empty character vector which results in a blank title.

To obtain a standard dialog box with 3-dimensional appearance, create a Form with Border set to 2 and EdgeStyle set to 'Dialog', for example:

  'F' ⎕WC 'Form' 'Dialog Box' ('EdgeStyle' 'Dialog')('Border' 2)

The State property has the value 0 if the window is currently displayed in its "normal" state, 1 if it is currently displayed as an icon, and 2 if it is currently maximised and displayed full-screen. This property does not just report the current state, but can be used to set the state under program control.

The VScroll and HScroll properties determine whether or not a Form has a vertical and horizontal scrollbar respectively. These properties are set to ¯1to obtain a scrollbar. Their default value is 0 (no scrollbar). VScroll and HScroll may only be set when the object is created and may not subsequently be changed. The Range property is a 2-element vector that specifies the maximum value for the vertical and horizontal scrollbars respectively. The PageSize property is a 2-element vector that specifies the sizes of the thumbs in each scrollbar. The Step property is a 4-element vector that specifies the sizes of the small and large change. Its first two elements refer to the vertical scrollbar, elements 3 and 4 refer to the horizontal scrollbar. The Thumb property is a 2-element vector that both reports and sets the position of the thumb in the vertical and horizontal scrollbars respectively. When the user attempts to move the thumb in one of the scrollbars, the Form generates a VScroll or HScroll event.

VScroll and HScroll cannot be changed using ⎕WS. However, you can make a scrollbar disappear by setting the corresponding element of Range to 1, thus allowing you to dynamically switch the scrollbar off and on. Note however that doing so will change the size of the Form.

Setting the FontObj property on a Form does not affect the text in its title bar. However, the value of FontObj will (unless over-ridden) be inherited by all of the objects within the Form.

The background of the Form may be coloured using BCol. The default value for BCol is the Windows Button Face colour unless EdgeStyle is set to 'None' or 'Default' in which case it is the Windows background colour. Alternatively, the background of a Form can be defined using a Bitmap or Metafile object whose name is defined by the Picture property. A Metafile is automatically scaled to fit the Form. A Bitmap can be tiled or scaled. See Picture property for details.

The OnTop property is either 0 or 1. If it is 0, the Form assumes its normal position within the stack of windows on the screen and is only brought to the front when it receives the input focus. If OnTop is set to 1, the Form is always brought to the front even when it doesn't have the focus. If more than one Form has OnTop set to 1, the stacking order of this set of Forms is defined by the order in which they were created.

A Form can be created as a child of another Form. If so, it has the following characteristics:

• A child Form always appears on top of its parent Form (although it is not constrained by it)
• When you minimize a parent Form, its child Forms disappear.
• Making the parent Form invisible or inactive has no effect on a Child Form.

Note that the Posn and Size properties of a child Form are expressed in screen coordinates and are not given relative to its parent.