Updated article: Using character escapes in markup and CSS

Numerous changes were made to this article to address feedback and also incorporate material on CSS escapes from the character encoding tutorial. This and other changes are described below. View the article.

German, Spanish, and Brazilian and Iberian Portuguese translators should consider updating it.

Description of changes:

• various parts of the text were rewritten
• the title and the question were changed
• the latest template was applied, and various new style conventions that affect the markup
• two new sections were added relating to CSS
• substantial changes were made to the Further Reading section

Translators should retranslate the whole article.