pdo as extension does not exist

In the documentation in almost all examples of building slim images the extension "pdo" is used - an example:

ARG PHP_EXTENSIONS="apcu mysqli opcache pdo pdo_mysql redis zip soap" directly under "Compiling extensions in the slim image".

But "pdo" is not a valid extension when trying to build the container - this is my output (for php 7.2 slim cli, the same with slim fpm):

Building container
Step 1/16 : ARG PHP_EXTENSIONS="opcache pdo pdo_mysql zip"
Step 2/16 : FROM thecodingmachine/php:7.2-v2-slim-cli
# Executing 7 build triggers
 ---> Using cache
 ---> Running in 548c6d0e99cd
Removing intermediate container 548c6d0e99cd
 ---> Running in ca7979a4a321
*** Installing extensions ***
The following extension(s) is not supported: pdo
Supported extensions: amqp, apcu, ast, bcmath, blackfire, bz2, calendar, dba, ds, enchant, ev, event, exif, gd, gettext, gmp, gnupg, igbinary, imagick, imap, intl, ldap, mailparse, mcrypt, memcached, mongodb, mysqli, opcache, pcntl, pcov, pdo_dblib, pdo_mysql, pdo_pgsql, pgsql, pspell, redis, shmop, snmp, soap, sockets, swoole, sysvmsg, sysvsem, sysvshm, tidy, wddx, weakref, xdebug, xmlrpc, xsl, yaml, zip

I suspect this is just a documentation error, but it is in all the examples and in the list of valid extensions, so it is likely people will stumble over it, as I did.

thecodingmachine / docker-images-php

pdo as extension does not exist #131