The CM search syntax allows for recursive searching, for example returning results from folders contained within folders. The operator that specifies recursion is the plus sign (+), the problem is that in a URL the plus sign is reserved to indicate white space.
To overcome this the ServiceAPI (and WebDrawer) use the tilde (~) instead of the plus sign, so instead of this:
If you would rather use a character (or sequence of characters) other than the tilde you can customise this in the hptrim.config. The Web Client, for example, uses _$_ instead of tilde, which is set in the 'searching' element in its hprmServiceAPI.config.
<searching pageSize="30" searchRecursiveOption="_$_"/>