This system-provided window procedure processes the actions on a multi-line entry field control (WC_MLE).

Purpose

A multi-line entry field control is a rectangular window that displays multiple lines of text that the operator can edit. When it has the focus, the cursor marks the current insertion or replacement point.

The text is displayed within a rectangular window. Scroll bars appear if requested.

On all four sides of the text within the window there exists a thin margin area. This margin remains drawn in the window's background color, and characters are never drawn into this margin. Mouse events that occur in the margin are processed differently from mouse events that occur in the text area. The margin should be large enough to be easily clicked on, but not so large as to take up a large quantity of screen space. It is suggested, but not required, that the left and right margins be half the average character width of the system font, and that the top and bottom margins be half the maximum baseline extent of the system font.

Text is defined as a stream of characters, with hard line-break characters in the text. Between any two bytes in the text stream, and at either end of the document, there is an insertion point. Note that in a DBCS environment, it is possible to have an insertion point in the middle of a DBCS character. If such an insertion point is specified in a function, the function will either round the insertion point in a sensible way, or the function will fail with an error code indicating the problem.

The text always contains a selection region, defined by an anchor point and a cursor point. The anchor and cursor points are insertion points. If the MLE window has the focus, the text between these two points is drawn highlighted and the cursor point is indicated by a flashing text cursor. The selection region can be affected by some import/export operations.

The cursor point and the anchor point define the range of the selection. These two points are often the same, in which case no text is selected and only a text cursor (but no highlighting) is displayed. A user can use SHIFT+cursor movement combinations to extend the selection, which leaves the anchor point alone, and moves the cursor point to a new position in the document.

The MLE has three modes:

INSERT/OVERTYPE

This mode determines whether keystrokes are inserted into the text, or whether they overtype existing text. Unlike the other two modes, this mode is maintained by the system. The MLE must merely be aware of the system mode.
READ-ONLY
The keyboard user interface disallows any operations that would change the content of the text, although applications using the MLE can still change the text contents. The application can query this mode, in order that it can disallow application-specific operations.
WORD-WRAP
When this mode is in effect, soft line-breaks are inserted into the text at word boundaries so that the user need not scroll the display horizontally to see all the text. When this mode is off, text is allowed to trail off the right-hand edge of the window.

Notes:

• The MLE is intended for text under 4Kb in size. Performance will be fast for text up to 32KB in size. Text greater than this will be supported but performance may not be acceptable.

• In this section 'CR' denotes carriage-return, and 'LF' denotes line-feed.

Multi-Line Entry Field Control Data

See MLECTLDATA for multi-line entry field control data.

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