Resources

Using Sane Defaults in Themes by Chip Bennett
Custom CSS boxes in themes by Justin Tadlock
A Guide to Writing Secure Themes – Part 1: Introduction by Fränk Klein
A Guide to Writing Secure Themes – Part 2: Validation by Fränk Klein
A Guide to Writing Secure Themes – Part 3: Sanitization by Fränk Klein
A Guide to Writing Secure Themes – Part 4: Securing Post Meta by Fränk Klein
When And How To Escape Core Functions In WPORG Themes by Milana Cap
List of functions that are escaped, from the WordPress Coding standardsWordPress Coding Standards The Accessibility, PHP, JavaScript, CSS, HTML, etc. coding standards as published in the WordPress Coding Standards Handbook. May also refer to The collection of PHP_CodeSniffer rules (sniffs) used to format and validate PHP code developed for WordPress according to the PHP coding standards..

Customizer

Customizer tutorials and documentation by Justin Tadlock
Moving to the Customizer API from the Settings API, using Options API by Chip Bennett

Review Videos

October 2016: Talking about escaping, validation and a few other things.
November 2016: Translation for themes and repo guidelines.
December 2016: Enqueuing scripts and stylesheets within WordPress and better practices for themes.
January 2017: Tools for reviewing themes: Local environments and testing tools.
February 2017: Hooks (Actions and Filters)

These licenses are GPLGPL GPL is an acronym for GNU Public License. It is the standard license WordPress uses for Open Source licensing https://wordpress.org/about/license/. The GPL is a ‘copyleft’ license https://www.gnu.org/licenses/copyleft.en.html. This means that derivative work can only be distributed under the same license terms. This is in distinction to permissive free software licenses, of which the BSD license and the MIT License are widely used examples. compatible and suitable for images:

CC0
CC BY 4.0
CC-BY-SA 4.0 – Compatible with the GPLv3 only.

If the license is not listed here, then it’s not compatible: https://www.gnu.org/licenses/license-list.html#GPLCompatibleLicenses

Recommended websites (for images):

wordpress.org/photos
Pexels Only CCO License, not the pexels licence.
- To find the license, click on the small link that says free to use. If the headline says “Legal Simplicity.” then the image uses the Pexels license. The limitations are listed in the second section.
stocksnap.io
skitterphoto.com
mystock.photos
pickupimage .com
pxhere.com
foodiesfeed.com
Smithsonian Open Access