Cross-community vote

A cross-community vote or cross-community support is a form of voting used in the Northern Ireland Assembly according to the provisions of the 1998 Good Friday Agreement. It requires the support of both main communities in Northern Ireland, in other words majority of unionists "and" the majority of nationalist members of the Assembly. Among other reasons, it arises when the petition of concern procedure is invoked.
Background.
Upon taking their seats members of the Northern Ireland Assembly are required to designate themselves as either "unionist", "nationalist" or "other". Members may change their designation of identity only if they become a member of a (different) political party or they cease to be a member of any political party.
The election of the Speaker, appointment of the Minister of Justice, any changes to the standing orders and the adoption of certain money bills must all occur with cross-community support.
This was originally set out in the Northern Ireland Act 1998.
Petition of concern.
Votes in the assembly do not ordinarily require cross-community support. However, if a "petition of concern" is raised successfully about proposed legislation or executive action, the speaker must call a cross-community vote. For a petition to be raised successfully, at least 30 of the 90 members must sign the petition. In a cross-community vote, the majority of unionists' "and" the majority of nationalists' votes are each required to pass a motion put to the assembly. , petitions of concern have been tabled 159 times since 1998; they have been used to block same-sex marriage, abortion law reform and even censure of politicians.
Section 42 of the 1998 Act declares that 
 However Standing Order 28 on Petitions of Concern does not mention this committee and () no such committee has been established. 
Arising from the St Andrews Agreement, an "Assembly and Executive Review Committee" was set up. Among its Terms of Reference, the Committee was to consider "provisions for voting on an Ad Hoc Committee on Conformity with Equality Requirements prior to the vote on a Petition of Concern." It also "considered the possibilities of restricting Petition of Concern to certain key areas, changing the 30 MLA threshold, and alternatives to Petitions of Concern (e.g. a weighted majority vote). There was no consensus on any of the issues.".
Procedure.
According to the standing orders of the assembly, "after the signing of the Roll a Member may enter in the Roll a designation of identity, being Nationalist, Unionist or Other. A Member who does not register a designation of identity shall be deemed to be designated Other for the purposes of these Standing Orders."
Designations.
"Note: These figures include the assumed designation of the Speaker who, having a non-partisan role, does not officially declare a designation. Note also the effect of the Reduction of Numbers Act, which partly accounts for the significant changes in 2017."
Parties.
List of current and previous assembly parties by designation.