From the way the pedaling is indicated it might seem that the strange pedaling indications does not involve signs U (heel). Instead, the toes are indicated v (left) or ^ (right), and the heels: ̺ (left), ̪ (right). Every sign is positioned BELOW the notes.
This might happen in some editions. If you are not aware of this difference, then it might even seem like some sort of early pedaling without heels is used. From this notation, it is certainly not very easy to decipher which foot (left or right) should play which note. That's the main difficulty, I think.
But in reality it is nothing more than a different form of notating heels and simply means that the heel is used in such cases. By the way, there was a time when it was common to use "o" sign for heels.
What to do if you are playing works of Mendelssohn or other composers from such editions? Is it practical nowadays when we all are used to modern pedaling signs?
What I have found from my own practice is that it takes more time to adjust to these pedaling signs but it certainly could be done.
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