docs($interpolate): add known issue about custom interpolation symbols

Closes #14610
Closes #6493

src/ng/interpolate.js

@@ -221,6 +221,25 @@ function $InterpolateProvider() {
      * symbol. For example, `{{ '}}' }}` will be incorrectly interpreted as `{{ ' }}` + `' }}`, i.e.
      * an interpolated expression consisting of a single-quote (`'`) and the `' }}` string.
      *
+     * @knownIssue
+     * All directives and components must use the standard `{{` `}}` interpolation symbols
+     * in their templates. If you change the application interpolation symbols the {@link $compile}
+     * service will attempt to denormalize the standard symbols to the custom symbols.
+     * The denormalization process is not clever enough to know not to replace instances of the standard
+     * symbols where they would not normally be treated as interpolation symbols. For example in the following
+     * code snippet the closing braces of the literal object will get incorrectly denormalized:
+     *
+     * ```
+     * <div data-context='{"context":{"id":3,"type":"page"}}">
+     * ```
+     *
+     * The workaround is to ensure that such instances are separated by whitespace:
+     * ```
+     * <div data-context='{"context":{"id":3,"type":"page"} }">
+     * ```
+     *
+     * See https://github.com/angular/angular.js/pull/14610#issuecomment-219401099 for more information.
+     *
      * @param {string} text The text with markup to interpolate.
      * @param {boolean=} mustHaveExpression if set to true then the interpolation string must have
      *    embedded expression in order to return an interpolation function. Strings with no