CSS glossary entries for ‘S’

Selection selector: The selection selector (E::selection) was a CSS ‘pseudo-element selector’ which appeared in earlier drafts of the CSS3 Selectors module. It is no longer documented and so may, presumably, ignored.
Selector: A selector is one of the 2 essential components of a CSS ‘rule’. It determines the set of elements within a web page that should be styled according to the instructions within that rule's ‘declaration’.
shape-image-threshold: The shape-image-threshold property is a CSS property which specifies the ‘alpha channel’ threshold used to extract a shape from an image as the value for ‘shape-outside’. A value of 0.75 means that the extracted shape will encapsulate all the pixels that are more than 75% opaque.
shape-margin: The shape-margin property is a CSS property which sets a margin on ‘shape-outside’.
shape-outside: The shape-outside property is a CSS property which uses shape values to define the ‘float area’ for a ‘float box’ and forces ‘inline content’ to wrap around the shape instead of the float's bounding box.
shorthand property: In CSS, a shorthand property is one which allows you to set many individual properties in one statements. Some shorthand properties will have no effect unless the designer gives values for all of the individual subsidiary properties, e.g. a browser cannot draw a border unless it knows the ‘border-style’ and the ‘border-color’ and the ‘border-width’ to use. On the other hand many shorthand properties such as ‘background’ and ‘list-style’ will have an effect if only one of their subsidiary values is set.
space-around value: When applied to a ‘flexible box’ alignment property, the space-around value ensures that layout lines within the flexible container are evenly distributed with equal space between them. Unlike ‘space-between’, this value ensures that there are spaces at the beginning and end of the box, equal to those between the lines.
space-between value: The space-between value is a CSS value for evenly distributed distributing the lines in a ‘flexible box’. In addition to equalising the spaces between lines, it dictates that the first line should appear right at the start of the container while the last one should be hard up against the end of the container. The space-between value can be set on properties that determine the alignment of lines within flexible boxes.
Square brackets: Square brackets (e.g.[]) are used in CSS to delimit the beginning and end of a pattern to be matched in an ‘attribute selector’, i.e. to select one or more elements based on the presence of a given attribute name or attribute ‘name-value pair’.
stretch value: When applied to a ‘flexible box’ alignment property, the CSS stretch value ensures that layout lines stretch to take up the remaining space within a flexible container.
Subject of selector: The subject of selector (E!>F) appeared in early drafts of the CSS4 Selectors module but seems to be missing from recent ones. It was supposed to allow you to style the parent or ancestor of selected page components; the exclamation mark indicating where the styling effect should be visible.
Subsequent sibling selector: Subsequent sibling selector is what we consider to be a more linguistically comfortable name for what the W3C CSS standard calls the ‘indirectly adjacent selector’. No doubt some grammarian will point out that you can be indirectly adjacent, in the same way that you can be half pregnant. We don't care.
Substring selector: The Substring selector (E[attr*="value"]) is a CSS ‘attribute selector’ which targets all the elements in a document which have the specified attribute, so long as the attribute's value contains the specified substring anywhere within it. The substring can occur in any position within the attribute value, and can have any character (or no characters) before or after it.