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diff --git a/devdoc/dw-fixed-positions.doc b/devdoc/dw-fixed-positions.doc new file mode 100644 index 00000000..d62565ff --- /dev/null +++ b/devdoc/dw-fixed-positions.doc @@ -0,0 +1,63 @@ +/** \page dw-fixed-positions Fixed positions + +In some cases, widgets or widget content must be positioned relative +to the viewport. As in the CSS specification, these positions will be +called "fixed positions". This must not be confused with "fixedly +positioned elements" (see \ref dw-out-of-flow), which are a special +case of fixed positions. + + +Applications +============ + +As defined by CSS +----------------- + +- "position: fixed"; see \ref dw-out-of-flow. +- "background-attachment: fixed"; see \ref dw-images-and-backgrounds. + +Idea for tables +--------------- + +Often, tables have a header, which contains informations necessary to +interpret the columns in the table body. For this, HTML defines the elements +<thead> and <tbody> +<sup><a href="#note-table-footer" id="ref-table-footer">[1]</a></sup>. + +For large tables, the problem occurs that the table header gets out of +the reader's view. In paged media, where a large table covers multiple +pages, this is often solved by *repeating* the table header on each +page occupied by the table. When using a viewport, a table larger than +the vieport could be displayed like this: + +1. If the top of the table is within the viewport, show the table + header at the usual position. +2. As soon as top of the table gets above the top border of the + viewport, keep the table header at the viewport top, so that it is + still visible (this means, it moves down, relative to the + *canvas*). This way, the header is still visible, so our objective + is achieved. +3. When scrolling further down, at some point the table body gets out + of the viewport again, and so should the table header. + +(Some images would be nice.) + +These ideas should be considered when developing a design for fixed +positions. + + +Design sketch +============== + +[...] + + +---------------------------------------------------------------------- + +<sup><a href="#ref-table-footer" id="note-table-footer">[1]</a></sup> +... and also <tfoot>, which is not discussed here, for reasons +of simplicity. However, it is obvious that <tfoot> should be +dealt with in an analogue way as <thead>. + + +*/
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