To come (publishing)
"To come" is a printing and journalism reference abbreviated "TK." It is used to signify that additional material will be added at a later date.
TK is a combination of letters designed to catch the eye (it is also likely to be caught by computer spell-check programs, though the use of TK long predates the use of computers.) It may originally have come into use because very few words feature the letter combination of "t" followed by "k". The phrase "to come," by contrast, could very easily be mistaken as a deliberate part of the text, especially if read by an overworked editor late at night while on deadline.
Occasionally an editor may mistakenly allow an article to be published with a stray TK intact, which is a source for much embarrassment and ridicule in the news room.
The Chicago Manual of Style online Q&A on manuscript preparation describes it as imprecise, stating, "It’s best to be more straightforward and specific. For example, use bullets or boldface zeros (••• or 000) to stand in for page numbers that cannot be determined until a manuscript is paginated as a book (but see paragraph 2.37 in CMOS). For items like missing figures, describe exactly what’s missing. In electronic environments, you have recourse to comment features—like the syntax of SGML, which allows for descriptive instructions that will not interfere with the final version of a document. Make sure that whatever you do stops the project in its tracks at some point before publication."
However, TK may be more useful in the magazine world because magazines consist of a greater variety of heterogeneous forms of copy written and edited by a larger number of people under tighter deadlines. Under those conditions, it is more natural and useful for participants to stick TK in "unthinkingly" to save time. In the magazine world, it is common for even important factual details not to be nailed down until quite late in the process, even as the magazine is being typeset. In the book world, most matters are decided well before the manuscript reaches the proof stage, and only such things as updated references would need a TK marker, while magazine workers might write a phrase like "...went to university TK years ago..." without having to puzzle out what form that TK should take (dots or zeroes?), full in the knowledge that everybody involved in the process knows what is meant, that further work is needed.