Special keys in a keyboard layout
A keyboard layout is any specific mechanical, visual, or functional arrangement of the keys, legends, or key–meaning associations (respectively) of a computer, typewriter, or other typographic keyboard.
1. Dead key
A dead key is a special kind of a modifier key that, instead of being held while another key is struck, is pressed and released before the other key.
The dead key does not generate a character by itself, but it modifies the character generated by the key struck immediately after, typically making it possible to type a letter with a specific diacritic.
For example, on some keyboard layouts, the acute accent key is a dead key; in this case, striking acute accent and then a results in á, whereas acute accent followed by e results in é. An acute accent in isolated form can be typed by striking acute accent and then space.
A key may function as a dead key by default, or sometimes a normal key can temporarily be altered to function as a dead key by simultaneously holding down the secondary-shift key (Alt Gr or option).
In some systems, there is no indication to the user that a dead key has been struck, so the key appears dead, but in some text-entry systems the diacritical mark is displayed along with an indication that the system is waiting for another keystroke: either the base character to be marked, an additional diacritical mark, or space to produce the diacritical mark in isolation.
Compared with the secondary-shift modifier key, the dead-key approach may be a little more complicated, but it allows of more additional letters. Using the secondary shift, you may only type one or (if you use it simultaneously with the normal shift key) two additional letters with each key, whereas using a dead key, a specific diacritic can be attached to a number of different base letters.
2. Compose key
A Compose key can be characterized as a generic dead key that may in some systems be available instead of or in addition to the more specific dead keys.
It allows access to a wide range of predefined extra characters by interpreting a whole sequence of keystrokes following it.
For example, striking compose followed by apostrophe and then a results in á, compose followed by a and then e results in æ, and compose followed by o and then c results in © (circled c, copyright symbol).
The Compose key is supported by the X Window System (used by most Unix-like operating systems, including most GNU/Linux distributions). Some keyboards have a key labelled "Compose", but any key can be configured to serve this function. The otherwise redundant right-hand Windows key is a common choice, when available.
3. Shift key
The shift key is a modifier key on a keyboard, used to type capital letters and other alternate "upper" characters.
There are typically two shift keys, on the left and right sides of the row below the home row.
The shift key's name originated from the typewriter, where one had to press and hold the button to shift up the case stamp to change to capital letters; the shift key was first used in the Remington No. 2 Type-Writer of 1878; the No. 1 model was capital-only.
On an English keyboard, characters that typically require the use of the shift key include the parentheses, the question mark, the exclamation point, and the colon.
When the caps lock key is engaged, the shift key can be used to type lowercase letters on most systems.
On computer keyboards, as opposed to typewriter keyboards, the shift key can have many more uses: It is sometimes used to modify the function keys.
Modern Microsoft Windows keyboards typically have only 12 function keys; Shift+F1 must be used to type F13, Shift+F2 for F14, etc. It can modify various control and alt keys. For example, if Alt-tab is used to cycle through open windows, Shift-Alt-tab cycles in the reverse order.
Holding shift while in a word processor will anchor the insertion point, such that moving the cursor and clicking the mouse to a new point will select the range of text in between.
Holding shift while drawing with the mouse in graphics programs generally confines the shape to a straight line, usually vertically or horizontally, or to draw squares and circles using the rectangle and ellipse tools, respectively.
The shift key can also be used to modify the mouse behavior on a computer. For example, holding shift while clicking on a link in a web browser might cause the page to open in a new window, or to be downloaded. In some Web browsers, holding shift while scrolling will scan through previously viewed Web pages.
StickyKeys is an accessibility feature to help computer users who have physical disabilities, but it is also used by others as a means to reduce RSI (or a syndrome called the Emacs Pinky).
It essentially serializes keystrokes instead of pressing multiple keys at a time: StickyKeys allows the user to press a modifier key, such as Shift, Ctrl, Alt, or the Windows key, and have it remain active until any other key is pressed.
5. Modifier keys
In computing, a modifier key is a special key on a computer keyboard that modifies the normal action of another key when the two are pressed in combination.
For example, Alt+F4 in Microsoft Windows will close the program in the active window; in this instance, Alt is the modifier key. In contrast, pressing just F4 will probably do nothing unless assigned a specific function in a particular program.
By themselves, modifier keys usually do nothing, that is, pressing Alt alone does not trigger any action from the computer. Modifier keys on personal computers The most common are: ⇧ Shift Ctrl Alt (Alternative) AltGr (Alternative Graphic) Super – called Windows key on Windows keyboards,
Cmd key on Mac OS computers or Meta key on SUN. Fn (Function) – present on small-layout keyboard, usually on notebooks. ⇧ Shift is the oldest in terms of keyboards in general as it originates from typewriters and is usually used to make uppercase letters when typing.
6. Function key
A function key is a key on a computer or terminal keyboard which can be programmed so as to cause an operating system command interpreter or application program to perform certain actions. On some keyboards/computers, function keys may have default actions, accessible on power-on. Usually, we call F1 to F12 as function keys.
7. Fn key
Fn, or 'Function', is a modifier key on many keyboards, especially on laptops, used in a compact layout to combine keys which are usually kept separate.
It is typically found on laptops, since a full sized keyboard would be difficult to fit in a laptop chassis. It is also found in many full-sized 'multimedia' and 'office' keyboards, named F-Lock key.
It is mainly for the purpose of changing display or audio settings quickly, such as brightness, contrast, or volume, and is held down in conjunction with the appropriate key to change the settings.
Not only in laptop keyboards, desktop keyboards are now set Fn. Those keyboards are mostly multimedia keyboards. Fn key allow those F1 to F12 function keys to active application as web, music, my computer, email and the like.
For some desktop keyboards, there have two Fn keys, one on the left and one on the right. The right Fn key can help active Pgun,Pgup by pressing the Fn and arrow keys at the same time.
Unlike other modifier keys such as Ctrl, Shift and AltGr, the microcontroller inside the keyboard typically sends out a different keycode depending on whether the Fn key is depressed. This allows the keyboard to emulate a full sized keyboard, so that specialised keymaps do not need to be created; the operating system can use standard keymaps designed for a full sized keyboard. Because the operating system has no notion of the Fn key, the key can not be remapped in software, unlike all other standard keyboard keys.
8. AltGr key
AltGr (also Alt Graph, Alt Grill, Alt Car or Alt Char) is a modifier key found on many computer keyboards and primarily used to type characters that are unusual for the locale of the keyboard layout, such as currency symbols and accented letters.
On a typical IBM compatible PC keyboard, the AltGr key, when present, takes the place of the right-hand Alt key. In Mac OS X, the Option key has functions similar to the AltGr key.
AltGr is effectively comparable with the Shift key, which can be used in combination with a character-printing key to type a second-level character – typically the uppercase variant of a letter.
With the help of the AltGr key, the same printing key can be used to produce a third-level character (which may be visible, sometimes in a different color, on the front vertical face or the bottom right of the key top).
Using AltGr and Shift together often provides access to even a fourth-level character.
For example, on the US-International keyboard layout, the C key can be used to insert four different characters:
C → c (lowercase)
⇧ Shift+C → C (uppercase)
AltGr+C → © (copyright sign)
AltGr+⇧ Shift+C → ¢ (cent sign)
Control + Alt as a substitute
Originally, US PC keyboards (specifically, the US 101-key PC/AT keyboards) did not have an AltGr key, it being relevant to only non-US markets; they simply had "left" and "right" Alt keys.
As those using such US keyboards increasingly needed the specific functionality of AltGr when typing non-English text, Windows began to allow it to be emulated by pressing the Alt key together with the Control key:
Ctrl+Alt ≈ AltGr
Therefore, it is recommended that this combination not be used as a modifier in Windows keyboard shortcuts as, depending on the keyboard layout and configuration, someone trying to type a special character with it may accidentally trigger the shortcut,or the keypresses for the shortcut may be inadvertently interpreted as the user trying to input a special character.