We're no longer able to specifically identify what level flowing liquids are at since 1.13.

Ever since the removal of "flowing_liquid" identifiers ("liquid" being either lava or water), presumably we're supposed to be using "liquid[level=#]" in order to detect the level in a particular voxel (especially since it tab-completes). But this unfortunately yields no result:

execute if block ~ ~ ~ lava
# Test Passes

execute if block ~ ~ ~ lava[level=6]
# Test Fails

It will detect if the flowing lava is lava at all, but will fail to identify if it's at a specific level or not.

I've also tried manually setting a voxel to "lava[level=6]", both while isolated and then while touching a lava source block, and both times it tries to spawn a level = 2 flowing_lava block instead and will never sustain (will either disappear or get overwritten by the attached source's flow after a second).