Read "The Maze of Sleep" at The Eldritch Dark:
Since this early poem from Clark Ashton Smith (CAS) is a single stanza quatrain, I'm going to reprint the entire original text from The Star-Treader and Other Poems (1912):
Sleep is a pathless labyrinth,
Dark to the gaze of moons and suns,
Through which the colored clue of dreams,
A gossamer thread, obscurely runs.
In the version of this poem that is available on The Eldritch Dark, as well as in Selected Poems (1971), line three has had a word substitution, so that the later version reads: "Through which the exile clue of dreams".
Since this is such a short poem, that minor update caught my attention, as it makes me curious about how CAS viewed his own verses over the course of his life, and how he wanted them to be experienced by future readers.
The original phrase "colored clue" is a bit vague, but not out-of-place in a poem about the nebulous world of sleep and dreams. The updated phrase "exile clue" has more precision, assuming that CAS intended his readers to think of a secondary definition of the noun "clue", which the Shorter Oxford English Dictionary (SOED) gives as "The thread of a story; a train of thought." Likewise, I believe CAS' choice of the word "exile" hinges on an adjectival definition of that word which the SOED gives as: "Thin in consistency; fine, tenuous, insubstantial."
In this context, the last two lines of the poem ("Through which the exile clue of dreams, / A gossamer thread, obscurely runs.") are quite powerful, given that the word "exile" is echoed by the following phrase "gossamer thread", and we exit with the phrase "obscurely runs" where the choice of the word "obscurely" builds upon the words and phrases that I've highlighted.
It seems to me that this small edit to a short poem is not insignificant. In making that simple change, CAS achieved a greater coherency around the central idea of "The Maze of Sleep", all the more impressive since the subject matter at hand (sleep and dreams) is inherently imprecise.