'block_pair' error in 'BreakMeshByBlockGenerator'

[RECHOA]

Hi all,
I used --mesh-only to run the following inputfile:

[Mesh]
  [gen]
    type = GeneratedMeshGenerator
    nx = 20
    ny = 20
    nz = 2
    zmax = 0.2
    dim = 3
  []
  [block1]
    type = SubdomainBoundingBoxGenerator
    block_id = 1
    bottom_left = '0 0 0'
    top_right = '0.5 1 0.2'
    input = gen
  []
  [block2]
    type = SubdomainBoundingBoxGenerator
    block_id = 2
    bottom_left = '0.5 0 0'
    top_right = '0.75 1 0.2'
    input = block1
  []
  [block3]
    type = SubdomainBoundingBoxGenerator
    block_id = 3
    bottom_left = '0.75 0 0'
    top_right = '1 1 0.2'
    input = block2
  []
  [breakmesh]
    input = block3
    type = BreakMeshByBlockGenerator
    #block_pairs = '2 1'
    #block_pairs = '2 3'
    block_pairs = '2 1 2 3'
  []
[]

In the object [breakmesh] with type = BreakMeshByBlockGenerator, if i used block_pairs = '2 1' or block_pairs = '2 3', it could create mesh correctly. However, if i used block_pairs = '2 1 2 3' or

    block_pairs = '2 1 
                   2 3'

it would fail with a message:

*** ERROR ***
param 'block_pair' not present in InputParams

Could you help me with this problem? Thanks in advance.

[RECHOA]

I got it. the block_pairs vector should be divided by a semicolon(;), for example:

    block_pairs = '2 1;
                   2 3'

Sorry i misunderstood the figure in https://mooseframework.inl.gov/source/meshgenerators/BreakMeshByBlockGenerator.html