Bug 249840

https://drafts.csswg.org/css-text-4/#valdef-text-wrap-balance

> balance

Same as wrap for inline boxes. For block containers that establish an inline formatting context, line breaks are chosen to balance the remaining (empty) space in each line box, if better balance than wrap is possible. This must not change the number of line boxes the block would contain if text-wrap were set to wrap.
The remaining space to consider is that which remains after placing floats and inline content, but before any adjustments due to text justification. Line boxes are balanced when the standard deviation from the average inline-size of the remaining space in each line box is reduced over the block (including lines that end in a forced break).

The exact algorithm is UA-defined.

UAs may treat this value as wrap if there are more than ten lines to balance.