Editing UTF-7 (section)

===Encoding===
First, an encoder must decide which characters to represent directly in ASCII form, which <code>+</code> have to be escaped as <code>+-</code>, and which to place in blocks of Unicode characters. The expansion cost of UTF-7 can be high: for example, the character sequence U+10FFFF U+0077 U+10FFFF is 9 bytes in UTF-8, but 17 bytes in UTF-7. (At worst, treating every codepoint as a sequence in its own right produces the maximum expansion of 5x, e.g. when encoding <code>@@</code> as <code>+AEA-+AEA-</code>.) Each Unicode sequence must be encoded using the following procedure, then surrounded by the appropriate delimiters.

Using the £† (U+00A3 U+2020) character sequence as an example:

{{ordered list
|1= Express the character's Unicode numbers (UTF-16) in binary:{{unbulleted list
|<samp>0x00A3 → 0000 0000 1010 0011</samp>
|<samp>0x2020 → 0010 0000 0010 0000</samp>}}
|2= Concatenate the binary sequences:<br />
<samp>0000 0000 1010 0011 and 0010 0000 0010 0000 → 0000 0000 1010 0011 0010 0000 0010 0000</samp>
|3= Regroup the binary into groups of six bits, starting from the left:<br />
<samp>0000 0000 1010 0011 0010 0000 0010 0000 → 000000 001010 001100 100000 001000 00</samp>
|4= If the last group has fewer than six bits, add trailing zeros:<br />
<samp>000000 001010 001100 100000 001000 00 → 000000 001010 001100 100000 001000 000000</samp>
|5= Replace each group of six bits with a respective Base64 code:<br />
<samp>000000 001010 001100 100000 001000 000000 → AKMgIA</samp>
}}