Create a custom escaping mode.
All modes escape &.
The mode can further be set to escape < and > (escapeLtGt),
" (escapeQuot), ' (escapeApos), and/or / (escapeSlash).
Source
const HtmlEscapeMode({String name: "custom",
this.escapeLtGt: false,
this.escapeQuot: false,
this.escapeApos: false,
this.escapeSlash: false}) : _name = name;