# What does “a drop in replacement” mean

Please see the second response here.

You should try xelatex which is almost a drop in replacement for latex.

Leaving aside the technical part, which of no interest to the general audience here, I am interested in knowing what does this "almost a drop in replacement" mean?

I have a general feeling that this means something which will eventually/easily replace something, but I may be wrong.

We have other questions (A, B) here on "drop", but they seem to be different.

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The correct phrase is drop-in replacement. –  helix Mar 26 '14 at 8:46

It is not (a drop) (in) (replacement), but rather (a) (drop in) (replacement).

It is such a good replacement that you could take away the original, drop in the replacement, and not notice it. Well, almost, according to the text.

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I searched google for the meaning of "drop-in" and what meaning I got is "visited on an informal basis without booking or appointments." And that meaning don't work here. So I am curious to known where from you got this meaning. –  Man_From_India Mar 27 '14 at 12:23
From usage. And yes, there are other meanings as well. Actually when I look on google, by far most of the links on the first page for drop in replacement fit the meaning I gave. I am actually wondering how much you tried to find an alternative, completely non-fitting menaning. Have a look at our neighbours at ELU. –  oerkelens Mar 27 '14 at 12:36
Only one I found - wordnik.com/words/drop-in –  Man_From_India Mar 27 '14 at 13:05
If you type define drop in replacement into google you will find tons of examples that use it in the sense that I explained :) –  oerkelens Mar 27 '14 at 13:13
There are two meanings of "drop in" that come to mind, and you've hit on them both. There is "drop in [to some place]", meaning to visit without booking. And there is "drop [something] in [to replace something else]", which is less common, except in idioms like "drop-in replacement". –  Tim Pederick May 11 '14 at 9:12

This is something of a technical idiom. If you have a system of parts (e.g. a home computer), and you can pick up one module (e.g. a RAM stick) and "drop in" a new one in its place without fiddling about (because the connections are the same and the two sticks are the same size), then the new RAM stick is a "drop-in replacement" for the old one.

The phrase has since been transplanted from the physical realm into the virtual one, where a piece of software or a piece of code or really anything modular can be "dropped in" to where you took out the original thing, without significant alteration or reconfiguration.

So, it expresses a one-shot, effortless replacement of a part.

In this case, the syntax of the two LaTeXes is similar enough that you can switch over without having to update your code.

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