static bool isValidColumnSpanner(RenderMultiColumnFlowThread* flowThread, RenderObject* descendant)
{
    // We assume that we're inside the flow thread. This function is not to be called otherwise.
    ASSERT(descendant->isDescendantOf(flowThread));

    // First make sure that the renderer itself has the right properties for becoming a spanner.
    RenderStyle& style = descendant->style();
    if (style.columnSpan() != ColumnSpanAll || !descendant->isBox() || descendant->isFloatingOrOutOfFlowPositioned())
        return false;

    RenderBlock* container = descendant->containingBlock();
    if (!container->isRenderBlockFlow() || container->childrenInline()) {
        // Needs to be block-level.
        return false;
    }

    // This looks like a spanner, but if we're inside something unbreakable, it's not to be treated as one.
    for (RenderBox* ancestor = toRenderBox(descendant)->parentBox(); ancestor; ancestor = ancestor->parentBox()) {
        if (ancestor->isRenderFlowThread()) {
            // Don't allow any intervening non-multicol fragmentation contexts. The spec doesn't say
            // anything about disallowing this, but it's just going to be too complicated to
            // implement (not to mention specify behavior).
            return ancestor == flowThread;
        }
        ASSERT(ancestor->style().columnSpan() != ColumnSpanAll || !isValidColumnSpanner(flowThread, ancestor));
        if (ancestor->isUnsplittableForPagination())
            return false;
    }
    ASSERT_NOT_REACHED();
    return false;
}
void RenderBoxModelObject::moveChildrenTo(RenderBoxModelObject* toBoxModelObject, RenderObject* startChild, RenderObject* endChild, RenderObject* beforeChild, bool fullRemoveInsert)
{
    // This condition is rarely hit since this function is usually called on
    // anonymous blocks which can no longer carry positioned objects (see r120761)
    // or when fullRemoveInsert is false.
    if (fullRemoveInsert && isRenderBlock()) {
        RenderBlock* block = toRenderBlock(this);
        block->removePositionedObjects(0);
        if (block->isRenderBlockFlow())
            toRenderBlockFlow(block)->removeFloatingObjects();
    }

    ASSERT(!beforeChild || toBoxModelObject == beforeChild->parent());
    for (RenderObject* child = startChild; child && child != endChild; ) {
        // Save our next sibling as moveChildTo will clear it.
        RenderObject* nextSibling = child->nextSibling();
        moveChildTo(toBoxModelObject, child, beforeChild, fullRemoveInsert);
        child = nextSibling;
    }
}