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A dropdown button triggers a panel with a disclosure or combobox. Which dropdown panel should you use? Text and icon dropdowns: A dropdown button uses the chevron-down icon to the right of the text label. The chevron is the only icon that should be present with a text label. Split dropdown: A dropdown button is split when additional related actions are available. The left half displays the default action and the additional related actions are contained within the attached dropdown on the right half. The options available in the dropdown perform the action on click. An icon can be used in place of text. Use a tooltip to provide context, unless the action may be universally understood, like a closing action using the close icon. An icon-only button shouldn’t be used to toggle between two states. If the icon and action of the button change after clicking it, it can be difficult to determine if the icon represents the current or future state.
Invisible buttons have a transparent background with translucent hover and active states, making them useful for compound components like ActionList. Danger buttons should be used sparingly to warn of a destructive action, typically resulting in the opening of a confirmation dialog. An inactive button has styles that make the button appear «muted». The style is the same for all button variants. An inactive button is an accessible alternative to a disabled button. They’re intended to be used for buttons that are non-functional, but cannot be removed from the page. Unlike a disabled button, an inactive button can respond to user input. For example, if a button shows a tooltip when hovered or focused, or a dialog when clicked. If you need to use an inactive button, it’s best to have something else on the page that informs users about the issue that broke the button’s normal functionality. For example, showing a global banner for service outages.
Don’t rely on these icons alone to convey meaning — make sure that the text label of the button provides sufficient meaning/context on its own. Button has different schemes/variants (such as danger, primary, invisible), which result in different text, background, and border colours. Note that these differences are purely visual — they may be difficult to distinguish for users with impaired color perception, and won’t be exposed at all to screen reader users. For this reason, you can’t rely on the scheme/variant alone to give meaning to your content. Make sure that the text label of the button provides sufficient meaning/context on its own, regardless of its visual presentation. The button must have a minimum target size of 24×24 CSS pixels. This is to ensure that the button is large enough to be easily activated by users with motor impairments. There are rare cases where it’s ok to disable a button, but it should generally be avoided.
The file function expands to the empty string when writing to a file. When reading from a file, the file function expands to the verbatim contents of the file, except that the final newline (if there is one) will be stripped. Attempting to read from a non-existent file expands to the empty string. When the file function is evaluated all its arguments are expanded first, then the file indicated by filename will be opened in the mode described by op. Without the ‘-n’ or ‘-q’ flag, when make is actually executing recipes, the ‘-W’ flag can direct make to act as if some files had been modified, without actually running the recipes for those files. Note that the options ‘-p’ and ‘-v’ allow you to obtain other information about make or about the makefiles in use (see Summary of Options). Sometimes you may have changed a source file but you do not want to recompile all the files that depend on it.
GOAL is invalid and will result in an error. This variable is set only if this instance of make has restarted (see How Makefiles Are Remade): it will contain the number of times this instance has restarted. Note this is not the same as recursion (counted by the MAKELEVEL variable). You should not set, modify, or export this variable. When make starts it will check whether stdout and stderr will show their output on a terminal. TERMERR, respectively, to the name of the terminal device (or true if this cannot be determined). If set these variables will be marked for export. These variables will not be changed by make and they will not be modified if already set. If you invoke a sub-make and redirect its stdout or stderr it is your responsibility to reset or unexport these variables as well, if your makefiles rely on them. The first character of the value of this variable is used as the character make assumes is introducing a recipe line.
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