Display arbitrary sidebar content conditional upon a particular post or page.
Aside widget allows a page or post to insert arbitrary content into a sidebar (or other dynamic widget area), supporting something similar to the typographic notion of a 'pull-quote'.
Aside widget is triggered by the presence, in those pages which require it, of one or more 'aside' custom fields with values that specify the content of one or more widgets. Shifting the locus of widget content control from the widget to the page makes for more natural authoring of conditional content which needs to be associated with just a small number of pages.
As well as text, an 'aside' custom field may contain HTML and/or PHP code. Of course, any HTML should be crafted so as not to break the containing page structure. PHP parsing must be explicitly enabled in the widget administration panel and any PHP in the 'aside' field value must be enclosed in the usual tags for it to be recognised.
A little bit of short-form magic can be triggered by formatting the aside field value in the following way.
A value of the form #id (e.g. '#232') causes the the page or post identified by the integer id to be used as the widget content.
A value of the form !id (e.g. '!myasidediv') causes the contents of the HTML DIV identified by id to be used as the widget content. The selected DIV must reside withing the current page or post. Normally, the selected DIV is removed from display within the page proper, but a value of the form !!id causes the DIV to remain in the normal page flow. Processing of page content for the identified DIV is unsophisticated: the DIV must not itself contain any other DIVs and the DIV id attribute must be the first attribute after the tag name.
Prefix and suffix can be used to specify arbitrary text/HTML which will be used to bracket the selected widget content. PHP can also be used, but will only work if parsing is enabled as described above.