Expandable indent storing additional block, which indent is used as min indent marker...

Expandable indent storing additional block, which indent is used as min indent marker for all children of blocks corresponding to particular expandable indent.

If all blocks corresponding to current expandable indent has no linefeeds in their whitespaces, if one of these blocks has child which has indent less or equal than min marker indent, than indent is expanded.

Total summary:
Indent is expanded, if any of blocks with these indent is located on new line, or when there is some block's children with indent less or equal than min marker indent.