"a very good explainer" is just a colloquial phrase, meaning "explanatory piece of expository writing."
I think you're just noticing and reacting to an example of the rather casual writing style that appears to be replacing the expected traditional presentation of pieces in The Economist.
I'm pretty sure s/he's from Earth, where use of language often changes not only according to geography but time, profession, or social milieu. Where is that not the case? Where is it traditional to go on so much about one phrase instead of addressing the ideas in an article? I don't think I'd want to live on Pedant Planet.
Although to be honest I would have read "a very good explainer" as being someone who is good at explaining rather than a thing. I don't believe "explainer" is a word in English.
Comments
"a very good explainer" is just a colloquial phrase, meaning "explanatory piece of expository writing."
I think you're just noticing and reacting to an example of the rather casual writing style that appears to be replacing the expected traditional presentation of pieces in The Economist.
Where are you from? To me (US), as apparently to grandparent, "a very good explainer" is an error, not a colloquialism.
UK here. It's definitely been in use as journalistic jargon for a while, typically in the form of a headline "Explainer: <topic of article>", e.g. http://www.theguardian.com/commentisfree/libertycentral/2009... (2009); here's a trend graph that shows that usage has picked up in the last decade: http://www.google.com/trends/explore#q=explainer
Earliest citation I've been able to find (1998): http://books.google.co.uk/books?id=kw9lAAAAMAAJ&q=%22an+expl... - note that this is US, not UK.
Article on "explainer" journalism; a little informal but demonstrates usage: http://www.theawl.com/2014/03/eleven-questions-about-explain...
Wow ... apparently I'm ignorant twice with this comment (at least the last one I made was well-received):
a) Culturally ignorant - I had no idea that "explainer" was in common use in the UK. I would have called the rest of the article "an explanation".
b) Literally ignorant - How did I miss that this wasn't an Economist article?
Sorry!
Here's a relatively recent example of it being used in US headline writing to mean an explanatory pamphlet -
"Republicans to Distribute Shutdown Explainer"
http://www.rollcall.com/news/republicans_to_distribute_shutd...
And here's another from The Washington Post, to mean the text of the article -
"Who is Daft Punk? A quick explainer for confused Grammy-watchers"
http://www.washingtonpost.com/blogs/style-blog/wp/2014/01/27...
I'm from the US, but "an explainer" is a UKism from what I know. I've seen it used elsewhere.
I'm pretty sure s/he's from Earth, where use of language often changes not only according to geography but time, profession, or social milieu. Where is that not the case? Where is it traditional to go on so much about one phrase instead of addressing the ideas in an article? I don't think I'd want to live on Pedant Planet.
"explanatory piece of expository writing."
Or "an explanation" in English.
Although to be honest I would have read "a very good explainer" as being someone who is good at explaining rather than a thing. I don't believe "explainer" is a word in English.