An MLE field contains one or more lines of text. Each line consists of one or more characters and ends with one or more characters that represent the end of the line. The end-of-line characters are determined by the format of the text.

The user can type text in an MLE field when the MLE field has the focus. The application can insert text at any time by using the MLM_INSERT message and specifying the text as a null-terminated string. The MLE field control inserts the text at the cursor position or replaces the selected text.

The MLE field control entry mode, insert or overstrike, determines what happens when the user inserts text. The user sets the entry mode by pressing the Insert key. The entry mode alternates each time the user presses Insert. When overstrike mode is enabled, at least one character is selected. This means that the MLM_INSERT message always replaces at least one character. If insert mode is enabled, the MLM_INSERT message replaces only those characters the user or application has selected. Otherwise, the MLE field makes room for the inserted characters by moving existing characters to the right, starting at the cursor position.

The cursor position, identified by a blinking bar, is specified as a character offset relative to the beginning of the text. The user can set the cursor position by using the mouse or Arrow keys to move the blinking bar. An application can set the cursor position by using the MLM_SETSEL message, which directs the MLE field control to move the blinking bar to a given character position. The MLM_SETSEL message also can set the selection.

The selection is one or more characters of text on which the MLE field control carries out an operation, such as deleting or copying. The user selects text by pressing the Shift key while moving the cursor or by pressing mouse button 1 while moving the mouse. The user also can select a word in a block of text by double-clicking on the word. An application selects text by using the MLM_SETSEL message to specify the cursor position and the anchor point. The selection is all the text between the cursor position and the anchor point. If the cursor position and anchor point are equal, there is no selection. An application can retrieve the cursor position, anchor point, or both, by using the MLM_QUERYSEL message.

The user can delete characters, one at a time, by pressing the Delete key or the Backspace key. Pressing the Delete key deletes the character to the right of the cursor; pressing the Backspace key deletes the character to the left of the cursor and changes the cursor position. An application can delete one or more characters by using the MLM_DELETE message, which directs the MLE field control to delete a specified number of characters, starting at the given position. This message does not change the cursor position. An application can delete selected text by using the MLM_CLEAR message.

An application can reverse the previous operation by using the MLM_UNDO message, which restores the MLE field to its previous state. This is a quick way to fix editing mistakes. However, not all operations can be undone.

The application determines whether the previous operation can be undone by using the MLM_QUERYUNDO message, which returns TRUE and indicates the type of operation that can be undone. Using the MLM_RESETUNDO message, an application can prevent a subsequent MLM_UNDO message from changing the state of an MLE field.