Computes break positions that prevent Orphan and Widow elements, according to the definitions on the boxes themselves.
An Orphan is an element pushed on its own page, with all other elements on the previous pages. This is commonly found in groups where the group-footer is pushed to the next page.
An Widow is an element left on the current page, where all other elements are pushed to the next page. This is commonly found for group-headers, where the group-body is pushed to the next page.
This step calculates the minimum required space that an element would consume if it honours the widow and orphan rules.
When computing the rules, all children are considered, as long as they do not opt-out of the processing. A box that opts out, has the 'widow-orphan-opt-out' flag set to true. In the simple set of rules, only block-level elements are considered to opt-in for widow and orphan processing.
For orphans, this step computes the minimum space the element requires to be safely placed on this page. If the elements occupying that space would trigger a manual page-break, the break overrides the orphan rule, and the space for the orphan processing is limited to the point of the manual break.
For widows, this step also computes the minimum space required to satisfy the constraint. Manual breaks override the widow constraint. During pagination, the pagination processor has to check all parents to see whether their widow constrains are still fulfilled.
If the sum of the widow and orphan constraints is larger than the computed size of the box, the box is considered unbreakable and behaves as if the "keep-together" flag has been set.
The widow-orphan calculation ignores the 'fixed-position' setting when calculating constraints. Combining a widow-orphan constraint with the fixed-position constrained yields undefined results. The widow and orphan constraint is only active for paginated reports. It has no effect on flow or streaming report outputs.