Standard exception and redirect responses make use of the HTML 3.2 doctype. This was introduced about 15 years ago in 5326664. Also, examples and other places specify the HTML 4.01 doctype.
Most modern websites make use of the HTML5 doctype with HTML5 specific contents (source) and Flask also recommends using HTML5 (source).
My suggestion would be to go through the code base and update all the doctypes to <!doctype html>.
Standard exception and redirect responses make use of the HTML 3.2 doctype. This was introduced about 15 years ago in 5326664. Also, examples and other places specify the HTML 4.01 doctype.
Most modern websites make use of the HTML5 doctype with HTML5 specific contents (source) and Flask also recommends using HTML5 (source).
My suggestion would be to go through the code base and update all the doctypes to
<!doctype html>.