====== Operators ======
  * ''='' late evaluation (expand variable when used)
  * '':='' immediately expand
  * ''+='' append (with space)
  * ''=+'' prepend (with space)
  * ''.='' append (without space)
  * ''=.'' prepend (without space)
  * ''?='' assign if no other value was assigned
  * ''??='' assign if no other value was assigned (lower priority than mentioned above)

Rethink usage of ''+='' and similar in local.conf. Example:
  * If ''+='' is parsed before ''?='', the latter will be omitted.
  * **Solution**: use ''_append'' to unconditionally appends a value (but add space before value).

====== SRC_URI_append ======

When multiple ''.bbappend''s adds patches, order of patching is wrong.

poky/meta/classes/patch.bbclass
<code python>
def src_patches(d, all=False, expand=True):
    import oe.patch
    return oe.patch.src_patches(d, all, expand)
</code>

poky/meta/lib/oe/patch.py
<code python>
def src_patches(d, all=False, expand=True):
    fetch = bb.fetch2.Fetch([], d)
    patches = []
    sources = []
    for url in fetch.urls:
        local = patch_path(url, fetch, workdir, expand)
        if not local:
            if all:
                local = fetch.localpath(url)
                sources.append(local)
            continue
...
        localurl = bb.fetch.encodeurl(('file', '', local, '', '', patchparm))
        patches.append(localurl)
    
    if all:
        return sources

    return patches
</code>