• Spec currently defines whitespace can exist, and in some cases must exist around the destination and title, in the parens: https://spec.commonmark.org/0.29/#inline-link
• I clarified the wording recently in Clarify wording in spec for character groups commonmark-spec#618
• But whitespace was used since the start: https://github.com/commonmark/commonmark-spec/blame/858a28941d0dd17c24b7240f21372652111bd38b/spec.txt#L7495

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The bug probably stems from here:

, which seems to include spaces and newlines but not tabs.

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This bug can be reproduced with the following permalink to the dingus: https://spec.commonmark.org/dingus/?text=tab%3A%20%5Bx%5D(%09y)%0Aspace%3A%20%5Bx%5D(%20y)%0A%0Atab%3A%20%5Bx%5D(y%09)%0Aspace%3A%20%5Bx%5D(y%20)%0A%0Atab%3A%20%5Bx%5D(%09%3Cy%3E)%0Aspace%3A%20%5Bx%5D(%20%3Cy%3E)%0A%0Atab%3A%20%5Bx%5D(y%09%22z%22)%0Aspace%3A%20%5Bx%5D(y%20%22z%22)%0A.

The expected behavior is that tabs and spaces behave the same.