Leaf carpets allow you to place torches on them, and allow fences to connect to them.

Quark version: r1.2-94
ARL version: 1.2-6
Forge version: 1.12-14.21.0.2328

Relevant class: BlockLeafCarpet

Adding just as a note: this may have relation to a change done in vanilla 1.12, where some block sections (like back side of a stair block) now connects to fences. Specifically:

• MC-2813 – Snow doesn't form / cannot be placed on upside on upside down slabs / stairs
• MC-8345 – Placing torch on backside of stairs impossible
• MC-9176 – Glass panes not correctly rendering with the back of stairs
• MC-10613 – Fence doesn't connect with stairs