It's been asserted in another answer here that:
Marxism is, of course, part of the spectrum of Liberal ideologies, though it is often maligned as being something 'other.'
Looking at the SEP page on Liberalism it does indeed start with spectrum-like notion:
Liberalism is more than one thing. On any close examination, it seems to fracture into a range of related but sometimes competing visions.
But Marxism is only mentioned once on the page, and not in an inclusive manner:
During and after the Second World War the idea that liberalism was based on inherently individualist analysis of humans-in-society arose again. Karl Popper’s The Open Society and its Enemies (1945) presented a sustained critique of Hegelian and Marxist theory and its collectivist and historicist, and to Popper, inherently illiberal, understanding of society.
So, in what sense is Marxism liberal and who considers it so? (By "who" I mean to ask if there any notable thinkers/theorists/movements etc. that hold such a view, i.e. classify Marxism as part of liberalism spectrum in some fashion.)
Clarification: since liberalism is a contested term, I'm being very liberal here in the sense that answers can pick their your favorite sense of "liberal" that might make the opening statement true. I.e. this isn't a "is Y an X: true or false?" kind of question, but "since by my choice of X I'm flummoxed by this statement that, I let you chose an X for which you think this is true, but please explain your reasoning." Of course, I expect an answer to still choose an X that is not completely idiosyncratic to this question, like say X = Marxism, making the statement trivially true, but some that is verifiable use of the term outside this question. I.e., if the answer is "it's true on Fox News because of the US usage of the terms", then that's a valid answer as far as I'm concerned, although a bit boring.