What Does \'3D\' Represent in HTML Email Code?

Non-ASCII Characters in HTML: Understanding "3D" in HTML

When examining the HTML code of an email, one may encounter numerous instances of the character sequence "3D". This is not a typical element of HTML and raises the question: what does it represent?

3D: A Form of Email Encoding

Contrary to popular belief, "3D" is not related to 3D graphics in HTML. Rather, it is an integral part of an email encoding system known as "quoted-printable."

Quoted-printable encoding plays a crucial role in email transportation by allowing non-ASCII characters to be represented using only ASCII characters. This is essential for ensuring that email content remains intact during transmission, regardless of the recipient's encoding standards.

How Quoted-Printable Works

In quoted-printable encoding, any non-standard email octet (such as a non-English letter or symbol) is replaced by an equals sign (=) followed by two hexadecimal digits that represent the octet's numerical value.

To safeguard the equals sign itself from being misinterpreted as a start of encoding, it is also encoded using quoted-printable: the hex digits corresponding to the ASCII value of an equals sign (61) are "3D".

Therefore, when you see "3D" in HTML email code, it indicates that the preceding equals sign is part of quoted-printable encoding and should not be mistaken for a math operator. This encoding ensures that non-ASCII characters are correctly displayed in your email client, preserving the intended appearance of the message.

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