The appearance of attack ads from deep-pocketed political committees seems to have caught Tom Knox's mayoral campaign off-guard - in about the same way that some advocates for campaign-finance limits were shocked, just shocked, that Knox is willing, and able, to try to spend his way into City Hall.

Both camps should have seen it coming - and neither has much cause to cry foul. Not yet, anyway.

The impact of big-money political spending has yet to play itself out in the Philadelphia primary. It's too early to speculate about what revisions, if any, might be warranted in the city's giving limits.

Right now, the rules hold individual donors to $5,000 per candidate each year; political committees, to $20,000.

Conventional wisdom says the giving limits handcuff Knox's opponents, since the U.S. Supreme Court says the rich can spend their personal fortunes in a run for office.

But Knox could wake up on the morning after the May 15 election to discover that his millions weren't enough. Democratic city voters, in their wisdom, could opt for another candidate who's not a government novice and whose record as a reformer can be measured in years, rather than TV commercials.

Sure, those voters are getting more help in sizing up Knox right now in the form of those attack ads. They're being put on the air by so-called "527" groups, independent political committees set up under the federal tax code section of that number.

These groups are not limited in what they can raise or spend on their own, providing they have no formal link to any candidate. They may annoy Knox, but they're not illegal.

It was Knox's millions that spurred the creation of at least two of these counter-campaign groups in an effort to level the playing field.

Do 527s circumvent the spirit of the city's campaign finance reforms? Unquestionably, since any no-holds-barred fund-raising risks a return to pay-to-play politics.

Any after-action review of the 2007 mayoral campaign should look at whether Philadelphia, by ordinance, should impose limits on these groups.

For now, voters need as much information as possible. First and foremost, they need to know who is giving money to these 527s.

In that vein, city election officials are right to insist that the 527s - Working People for Truth of Washington, D.C., and the locally based Economic Justice Coalition for Truth - report their contributors tomorrow, as candidates must. Even better if the city were to insist that the 527s report every donation of more than $500 in the waning days of this campaign.

Kudos, also, to the city's Board of Ethics for scrambling to confirm that neither 527 is linked to a mayoral candidate. That would be illegal.