Adding my voice to insist that things are not that easy -- strictly speaking:

• HTML5 is a language specifications
• it could be serialized either as HTML or as XML

Case 1 : HTML serialization

(the most common)

If you serialize your HTML5 as HTML, "the text must not contain the character U+003C LESS-THAN SIGN (<) or an ambiguous ampersand."

An ambiguous ampersand is an "ampersand followed by one or more alphanumeric ASCII characters, followed by a U+003B SEMICOLON character (;)"

Furthermore, "the parsing of certain named character references in attributes happens even with the closing semicolon being omitted."

So, in that case editable && copy (notice the spaces around &&) is valid HTML5 serialized as HTML construction as none of the ampersands is followed by a letter.

As a counter example: editable&&copy is not safe (even if this might work) as the last sequence &copy might be interpreted as the entity reference for ©

Case 1 : XML serialization

(the less common)

Here the classic XML rules apply. For example, each and every ampersand either in the text or in attributes should be escaped as &.

In that case && (with or without spaces) is invalid XML. You should write &&

Tricky, isn't it ?