before 3.10/4.0 this override rule wold trigger on the entire subtree containing matching the condition:

[left_column_top_images2]
Source=left_column_top.tpl
MatchFile=left_column/top_images.tpl
Subdir=templates
Match[url_alias]=contact

these URLS's would trigger this rule, indenpendent of the translation (language) of the node specified in the condition:
example.com/eng/Contact
example.com/eng/Contact/English
example.com/eng/Contact/Support/Technical
example.com/ger/Kontact/Supporten/Technische
...because the "Contact" node was stored with the string "contact" ("/contact/") in the path_identification_string field in the ezcontentobject_tree table, where the condition looks up a potential match.
the "Kontact/Supporten/Technische" node would be stored as "/contact/support/technical/" in the ezcontentobject_tree table, and as such be a match for the "Match[url_alias]=contact" conditon.

this will not work after a 3.10 / 4.0 upgrade, since the Multiple URL Alias feature now uses language-specific aliases.
now the conditions will have be specified per language:

#English
[left_column_top_images2]
Source=left_column_top.tpl
MatchFile=left_column/top_images.tpl
Subdir=templates
Match[url_alias]=Contact

#German
[left_column_top_images2]
Source=left_column_top.tpl
MatchFile=left_column/top_images.tpl
Subdir=templates
Match[url_alias]=Kontact

problem:
a site that has a lot of override rules that depends on the old url_alias condition behavior, now have to add override rules for each language. if you have a lot of languages installed, then you suddenly get a lot of work ahead of you.

the conditions "node_id" and "parent_node" is not good enough, as they do not include the entire subtree for the given node.
the condition "section" requires a lot of policy changes and sectioning in the content, and is therfore impractical if you have many rules to replace.

solution:
we suggest that we add a new condition to the template override feature, that is language independent, and triggers on all subtrees of a given node.

the easiest way to implement this enhancement is to use the "path_string" field in the ezcontentobject_tree table, which is node ID based (as opposed to node name based) and is a part of all nodes below the one specified.

it will as such behave as url_alias condition used to do.

example:

#German
[left_column_top_images2]
Source=left_column_top.tpl
MatchFile=left_column/top_images.tpl
Subdir=templates
Match[path_string]=/1/2/4/5/

if node "contact" had path_string "/1/2/4/5/" then all nodes under this node would also have this path string included in their own path_string:
examples:
example.com/eng/Contact -> /1/2/4/5/
example.com/eng/Contact/English -> /1/2/4/5/89/
example.com/eng/Contact/Support/Technical -> /1/2/4/5/50/53/
example.com/ger/Kontact/Supporten/Technische -> /1/2/4/5/50/42