Question: Why should visitors check the rules before crossing the border?
About the article "Victoria Falls", section "Tourism in recent years".

Candidate passages:
By the end of the 1990s almost 300,000 people were visiting the falls annually, and this was expected to rise to over a million in the next decade.
Unlike the game parks, Victoria Falls has more Zimbabwean and Zambian visitors than international tourists; the attraction is accessible by bus and train, and is therefore comparatively inexpensive to reach.
The two countries permit tourists to make day trips from each side and visas can be obtained at the border posts.
Costs vary from US$45-US$80 (as of 01 December 2013).
Visitors with single entry visas will need to purchase a visa each time they cross the border.
Regular changes in visa regulations mean visitors should check the rules before crossing the border.
A famous feature is the naturally formed Devil's Pool, near the edge of the falls on Livingstone Island on the Zambian side.
When the river flow is at a certain level, usually between September and December, a rock barrier forms an eddy with minimal current, allowing adventurous swimmers to splash around in relative safety a few feet from the point where the water cascades over the falls.
Occasional deaths have been reported when people have slipped over the rock barrier.
The numbers of visitors to the Zimbabwean side of the falls has historically been much higher than the number visiting the Zambia side, due to the greater development of the visitor facilities there.
However, the number of tourists visiting Zimbabwe began to decline in the early 2000s as political tensions between supporters and opponents of president Robert Mugabe increased.
In 2006, hotel occupancy on the Zimbabwean side hovered at around 30%, while the Zambian side was at near-capacity, with rates in top hotels reaching US$630 per night.
The rapid development has prompted the United Nations to consider revoking the Falls' status as a World Heritage Site.
In addition, problems of waste disposal and a lack of effective management of the falls' environment are a concern.
Before the implementation of the Schengen Agreement, most borders in Europe were patrolled and a vast network of border posts existed around the continent, to check the identity and entitlement of people wishing to travel from one country to another.
Since the implementation of the Schengen rules, border posts have been closed (and often entirely removed) between participating countries.
The "Schengen Borders Code" requires participating states to remove all obstacles to free traffic flow at internal borders.
Thus, road, rail and air passengers no longer have their identity checked by border guards when travelling between Schengen countries, although security controls by carriers are still permissible.
Travellers should still bring a passport or a national identity card, and it might be required. 
All persons crossing external borders – inbound or outbound – have to be subject to at least a "minimum check", although travellers who are neither EU, EEA or Swiss citizens nor their family members enjoying the right of free movement must, in general, be subject to a "thorough check".
The only exception is for regular cross-border commuters (both those with the right of free movement and third-country nationals) who are well known to the border guards: once an initial check has shown that there is no alert on record relating to them in the Schengen Information System or national databases, they can only be subject to occasional 'random' checks, rather than systematic checks every time they cross the border.
In 'exceptional' and 'unforeseen' circumstances where waiting times become excessive, external border checks can be relaxed on a temporary basis.
Border guards carry out the following procedures when checking travellers who cross external borders:As shown by the table above, because many procedures are optional, border guards have discretion in deciding how rigorously they check travellers at external border crossing points.
As a result, the length of time taken to perform checks differs between Schengen countries.
For example, an entry check for an EU, EEA or Swiss citizen takes around 5 seconds on average in Italy, whilst in Norway, on average it takes around 1-minute.
The disparities in checks on third-country nationals are even greater.
For example, an entry check for an Annex II national takes around 15 seconds on average in Greece, whilst it takes 3–5 minutes on average in Slovakia.
Similarly, an entry check for an Annex I national on average lasts around 30–60 seconds in The Netherlands, whilst in Latvia, it lasts around 2–5 minutes on average.
When carrying out checks at external borders, border guards are, by law, required to respect the dignity of travellers (particularly in cases involving vulnerable persons) and are forbidden from discriminating against persons based on their sex, racial or ethnic origin, religion or belief, disability, age or sexual orientation.
External border controls are located at roads crossing a border, at airports, at seaports and on board trains.
Usually, there is no fence along the land border, but there are exceptions like the Ceuta border fence, and some places at the eastern border.
However, surveillance camera systems, some equipped with infrared technology, are located at some more critical spots, for example at the border between Slovakia and Ukraine, where at some points there is a camera every .
All travellers arriving from outside the Schengen Area using their own air plane or boat, have to go directly to an airport or seaport having a border control.
This is a loophole hard to check, and large-scale drug smuggling using sail boats has been found.
Along the southern coast of the Schengen countries, coast guards make a substantial effort to prevent private boats from entering without permission.
At many external border crossing points, there are special lanes for EU, EEA and Swiss citizens (as well as their family members) and other lanes for all travellers regardless of nationality.
At some external border crossing points, there is a third type of lane for travellers who are Annex II nationals (i.e.
non-EU/EEA/Swiss citizens who are exempt from the visa requirement).
Although Andorran and San Marinese citizens are not EU or EEA citizens, they are nonetheless able to use the special lanes designated for EU, EEA and Swiss citizens.
At the following external border crossing points, automated border gates are available for EU, EEA and Swiss citizens aged 18 or over holding biometric passports: : Prague Václav Havel Airport : Tallinn Airport : Helsinki Airport, Port of Helsinki and Vaalimaa (Also available for holders of Japanese biometric passports at Helsinki Airport.)
: Marseille Provence Airport, Paris-Charles de Gaulle Airport and Paris-Orly Airport (Also available for holders of EU, EEA and Swiss non-biometric machine readable passports, as well as family members of EU, EEA and Swiss citizens holding a residence permit marked 'Family member of EU citizen'.
All users who do not hold a French biometric passport need to register first.)
: Frankfurt Airport : Amsterdam Schiphol Airport : Oslo Airport, Gardermoen : Funchal Airport, Lisbon Portela Airport, Ponta Delgada Airport, Porto Airport : Barcelona El Prat Airport, Madrid-Barajas Airport (Also for holders of a Spanish identity card) : Zürich Airport Sometimes, external border controls are located on non-Schengen territory, but inside the EU.
For example, France operates border checks at juxtaposed controls on travellers departing the United Kingdom for the Schengen Area before they board their train or ferry at St Pancras International, Ebbsfleet International and Ashford International railway stations, as well as at the Port of Dover and Cheriton Eurotunnel terminal.
And some British border controls are located in France and Belgium.
The Schengen rules require that all passenger carriers across the Schengen external border must check, before boarding, if the passenger has the travel document and visa required for entry.
This is to prevent persons from applying for asylum at the passport control after landing within the Schengen Area. 
The Taba Border Crossing (, ) is an international border crossing between Taba, Egypt, and Eilat, Israel.  
A Border Crossing Card (BCC) is a document that allows limited entry into the United States by visitors.
The cards authorize visits to the border areas of the United States for a set amount of time.
Section 104 of the United States Illegal Immigration Reform and Immigrant Responsibility Act of 1996 (IIRIRA) serves as the legal basis for the issuance of Border Crossing Cards.