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21.7.4 Click Events

When the user presses a mouse button and releases it at the same location, that generates a click event. All mouse click event share the same format:

     (event-type position click-count)
event-type
This is a symbol that indicates which mouse button was used. It is one of the symbols mouse-1, mouse-2, ..., where the buttons are numbered left to right.

You can also use prefixes ‘A-’, ‘C-’, ‘H-’, ‘M-’, ‘S-’ and ‘s-’ for modifiers alt, control, hyper, meta, shift and super, just as you would with function keys.

This symbol also serves as the event type of the event. Key bindings describe events by their types; thus, if there is a key binding for mouse-1, that binding would apply to all events whose event-type is mouse-1.

position
This is a mouse position list specifying where the mouse click occurred; see below for details.
click-count
This is the number of rapid repeated presses so far of the same mouse button. See Repeat Events.

To access the contents of a mouse position list in the position slot of a click event, you should typically use the functions documented in Accessing Mouse. The explicit format of the list depends on where the click occurred. For clicks in the text area, mode line, header line, or in the fringe or marginal areas, the mouse position list has the form

     (window pos-or-area (x . y) timestamp
      object text-pos (col . row)
      image (dx . dy) (width . height))

The meanings of these list elements are as follows:

window
The window in which the click occurred.
pos-or-area
The buffer position of the character clicked on in the text area; or, if the click was outside the text area, the window area where it occurred. It is one of the symbols mode-line, header-line, vertical-line, left-margin, right-margin, left-fringe, or right-fringe.

In one special case, pos-or-area is a list containing a symbol (one of the symbols listed above) instead of just the symbol. This happens after the imaginary prefix keys for the event are registered by Emacs. See Key Sequence Input.

x, y
The relative pixel coordinates of the click. For clicks in the text area of a window, the coordinate origin (0 . 0) is taken to be the top left corner of the text area. See Window Sizes. For clicks in a mode line or header line, the coordinate origin is the top left corner of the window itself. For fringes, margins, and the vertical border, x does not have meaningful data. For fringes and margins, y is relative to the bottom edge of the header line. In all cases, the x and y coordinates increase rightward and downward respectively.
timestamp
The time at which the event occurred, as an integer number of milliseconds since a system-dependent initial time.
object
Either nil if there is no string-type text property at the click position, or a cons cell of the form (string . string-pos) if there is one:
string
The string which was clicked on, including any properties.
string-pos
The position in the string where the click occurred.

text-pos
For clicks on a marginal area or on a fringe, this is the buffer position of the first visible character in the corresponding line in the window. For other events, it is the current buffer position in the window.
col, row
These are the actual column and row coordinate numbers of the glyph under the x, y position. If x lies beyond the last column of actual text on its line, col is reported by adding fictional extra columns that have the default character width. Row 0 is taken to be the header line if the window has one, or the topmost row of the text area otherwise. Column 0 is taken to be the leftmost column of the text area for clicks on a window text area, or the leftmost mode line or header line column for clicks there. For clicks on fringes or vertical borders, these have no meaningful data. For clicks on margins, col is measured from the left edge of the margin area and row is measured from the top of the margin area.
image
This is the image object on which the click occurred. It is either nil if there is no image at the position clicked on, or it is an image object as returned by find-image if click was in an image.
dx, dy
These are the pixel coordinates of the click, relative to the top left corner of object, which is (0 . 0). If object is nil, the coordinates are relative to the top left corner of the character glyph clicked on.
width, height
These are the pixel width and height of object or, if this is nil, those of the character glyph clicked on.

For clicks on a scroll bar, position has this form:

     (window area (portion . whole) timestamp part)
window
The window whose scroll bar was clicked on.
area
This is the symbol vertical-scroll-bar.
portion
The number of pixels from the top of the scroll bar to the click position. On some toolkits, including GTK+, Emacs cannot extract this data, so the value is always 0.
whole
The total length, in pixels, of the scroll bar. On some toolkits, including GTK+, Emacs cannot extract this data, so the value is always 0.
timestamp
The time at which the event occurred, in milliseconds. On some toolkits, including GTK+, Emacs cannot extract this data, so the value is always 0.
part
The part of the scroll bar on which the click occurred. It is one of the symbols handle (the scroll bar handle), above-handle (the area above the handle), below-handle (the area below the handle), up (the up arrow at one end of the scroll bar), or down (the down arrow at one end of the scroll bar).