This template leaves leading space before the apostrophe, unlike the similar {{`}} (no spacing). This template is intended for use with italic text, whereas {{`}} is intended for use with non-italic text. For example:
The ''Iliad''{{'}}s vocabulary is archaic.
generates:
The Iliad's vocabulary is archaic.
with a tiny amount of space before the apostrophe to avoid colliding with the italic d at the end of Iliad.
This template is also similar to {{-'}}, used to slightly space apart a leading single quote from a surrounding double quotation mark provided by a template parameter in which the content is placed, e.g. the |title= parameter of {{cite web}}. The equivalent template when manually placing double quotes around a single-quoted passage is {{" '}}; see also {{'-}} and {{' "}} for the right-hand side equivalents (parameter and manual, respectively). All of these templates use 0.2 em of spacing, while this template, {{'}}, uses only 0.1 em of spacing, as does {{'s}}, which is used for possessives in italics.
