Derrida once explained that this assertion [means] there is nothing
outside context.
source - https://en.wikipedia.org/wiki/Jacques_Derrida#Philosophy
So inasmuch as literary criticism and philosophy are different contexts one might suppose the phrase could be taken and developed differently. However, the original context is Derridean and quite specific. By observing as far as possible the source the original meaning is protected. Where it is taken next, or whether it is deconstructed in situ, is something further.
Of Grammatology, page 158 - http://www.mohamedrabeea.com/books/book1_3997.pdf
the reading must always aim at a certain relationship, unperceived by
the writer, between what he commands and what he does not command of
the patterns of the language that he uses. This relationship is not a
certain quantitative distribution of shadow and light, of weakness or
of force, but a signifying structure that critical reading should
produce.
What does produce mean here? In my attempt to explain that, I
would initiate a justification of my principles of reading. A
justification, as we shall see, entirely negative, outlining by
exclusion a space of reading that I shall not fill here: a task of
reading.
To produce this signifying structure obviously cannot consist
of reproducing, by the effaced and respectful doubling of commentary,
the conscious, voluntary, intentional relationship that the writer
institutes in his exchanges with the history to which he belongs
thanks to the element of language. This moment of doubling commentary
should no doubt have its place in a critical reading. To recognize and
respect all its classical exigencies is not easy and requires all the
instruments of traditional criticism. Without this recognition and
this respect, critical production would risk developing in any
direction at all and authorize itself to say almost anything. But this
indispensable guardrail has always only protected, it has never
opened, a reading.
Yet if reading must not be content with doubling the text, it cannot
legitimately transgress the text toward something other than it,
toward a referent (a reality that is metaphysical, historical,
psychobiographical, etc.) or toward a signified outside the text whose
content could take place, could have taken place outside of language,
that is to say, in the sense that we give here to that word, outside
of writing in general. That is why the methodological considerations
that we risk applying here to an example are closely dependent on
general propositions that we have elaborated above; as regards the
absence of the referent or the transcendental signified. There is
nothing outside of the text [there is no outside-text; il n’y a pas de
hors-texte]. And that is neither because Jean-Jacques’ life, or the
existence of Mamma or Thérèse themselves, is not of prime interest to
us, nor because we have access to their so-called “real” existence
only in the text and we have neither any means of altering this, nor
any right to neglect this limitation. ...