I wrote this sentence
After providing the anchors, the user must now specify the blocks of the page that are distinguished by one or a group of anchors (see Figure 4). Throughout this article, we refer to such block or range of nodes with the term context node.
Is it such block, or such a block?! I prefer not to say “such blocks”.
Because I’ve usually heard such a with adjectives like “such a nice boy”
If “block” is singular you need the article:
…we refer to such a block or…
Saying “such blocks” would also be correct, but as you say, you would prefer not to use that, so “such a block” would be your best bet.