There is an apostrophe instead of a single quote bounding one word that should be in quotes. This is on line 220 of https://svnweb.freebsd.org/doc/head/en_US.ISO8859-1/books/porters-handbook/slow-porting/chapter.xml?view=markup.
Created attachment 167182 [details] Mismatched Quote Fix
Thanks for the report!
A commit references this bug: Author: jgh Date: Fri Feb 19 19:59:43 UTC 2016 New revision: 48206 URL: https://svnweb.freebsd.org/changeset/doc/48206 Log: - address grammar PR: 207340 Submitted by: beryleo@gmail.com Approved by: bcr (mentor) Differential Revision: https://reviews.freebsd.org/D5351 Changes: head/en_US.ISO8859-1/books/porters-handbook/slow-porting/chapter.xml