Regex to match a set of words--but only if they don't appear at the beginning of the string or line

words-to-lowercase-regex.js

/**
 * When formatting a string in title case, we capitalize the all words except articles, conjunctions, 
 * copulae (forms of "to be"), and prepositions (with four or fewer characters).
 * The first and last words are always capitalized.
 *
 * Source: https://en.wikipedia.org/wiki/Letter_case#Title_case
 *
 * This regex uses a negative lookahead to only match the keywords if they aren't at the beginning of a line.
 * Note that this regex uses the multiline flag, indicating to match each line, not just the entire string.
 *
 * Additional resources:
 * - https://titlecaseconverter.com
 * - https://saijogeorge.com/title-case-converter/
 */

/(?<!^)(\b(A|Am|Amid|An|And|Are|As|At|Atop|Be|Been|But|By|Down|For|From|In|Into|Is|Like|Mid|Near|Next|Nor|Of|Off|On|Onto|Or|Out|Over|Past|Per|Plus|Pro|Sans|Save|So|Than|The|Till|To|Unto|Up|Upon|Via|Vice|Vs|Was|Were|With|Yet)\b)+/gm