What Does \'3D\' Mean in HTML Email Source Code?

Decoding the Mysterious "3D" in HTML Source Code

When examining the HTML code of a mailer in Gmail, one may encounter lines like these:

<td>

The presence of "3D" within the style attribute is puzzling. Is it a special rendering feature for email?

The Solution: Quoted-Printable Encoding

The mystery of "3D" lies in the use of quoted-printable encoding, a system that allows non-ASCII characters to be represented as ASCII for email transportation.

How It Works:

• Non-standard email octets (representing special characters, etc.) are encoded as an "=" sign followed by two hex digits representing their numerical value.
• To represent a plain "=" in email, it must also be encoded using quoted-printable: 3D are the hex digits corresponding to the ASCII value of "=" (61).

Example:

The "A0" shown in the HTML above represents a non-breaking space. In quoted-printable, this would be encoded as:

=A0

And to represent "=" itself, it would be encoded as:

3D

Therefore, the "3D" in the HTML code you encountered is not a 3D rendering feature but a part of the quoted-printable encoding process. It represents the "=" character used to introduce encoded non-ASCII characters.

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